14 changed files with 431 additions and 1905 deletions
--- a/.github/FUNDING.yml
+++ b/.github/FUNDING.yml
@ -1 +0,0 @@
-github: [alexflint]
--- a/.github/workflows/go.yml
+++ b/.github/workflows/go.yml
@ -15,17 +15,17 @@ jobs:
    strategy:
      fail-fast: false
      matrix:
-        go: ['1.20', '1.21', '1.22']
+        go: ['1.13', '1.14', '1.15', '1.16']

    steps:
    - id: go
      name: Set up Go
-      uses: actions/setup-go@v5
+      uses: actions/setup-go@v1
      with:
        go-version: ${{ matrix.go }}

    - name: Checkout
-      uses: actions/checkout@v4
+      uses: actions/checkout@v2

    - name: Build
      run: go build -v .
--- a/19
+++ b/19
@ -1,19 +0,0 @@
-all: goimports vet
-
-clean:
-	rm -f go.*
-
-redomod:
-	rm -f go.*
-	GO111MODULE= go mod init
-	GO111MODULE= go mod tidy
-
-test:
-	go test
-
-vet:
-	@GO111MODULE=off go vet
-	@echo this go binary package builds okay
-
-goimports:
-	goimports -w *.go
--- a/README.md
+++ b/README.md
@ -64,7 +64,7 @@ fmt.Println("Input:", args.Input)
 fmt.Println("Output:", args.Output)
 ```

-```shell
+```
 $ ./example src.txt x.out y.out z.out
 Input: src.txt
 Output: [x.out y.out z.out]
@ -80,12 +80,12 @@ arg.MustParse(&args)
 fmt.Println("Workers:", args.Workers)
 ```

-```shell
+```
 $ WORKERS=4 ./example
 Workers: 4
 ```

-```shell
+```
 $ WORKERS=4 ./example --workers=6
 Workers: 6
 ```
@ -100,12 +100,12 @@ arg.MustParse(&args)
 fmt.Println("Workers:", args.Workers)
 ```

-```shell
+```
 $ NUM_WORKERS=4 ./example
 Workers: 4
 ```

-You can provide multiple values in environment variables using commas:
+You can provide multiple values using the CSV (RFC 4180) format:

 ```go
 var args struct {
@ -115,50 +115,12 @@ arg.MustParse(&args)
 fmt.Println("Workers:", args.Workers)
 ```

-```shell
+```
 $ WORKERS='1,99' ./example
 Workers: [1 99]
 ```

-Command line arguments take precedence over environment variables:
-
-```go
-var args struct {
-	Workers int `arg:"--count,env:NUM_WORKERS"`
-}
-arg.MustParse(&args)
-fmt.Println("Workers:", args.Workers)
-```
-
-```shell
-$ NUM_WORKERS=6 ./example
-Workers: 6
-$ NUM_WORKERS=6 ./example --count 4
-Workers: 4
-```
-
-Configuring a global environment variable name prefix is also possible:
-
-```go
-var args struct {
-	Workers int `arg:"--count,env:NUM_WORKERS"`
-}
-
-p, err := arg.NewParser(arg.Config{
-    EnvPrefix: "MYAPP_",
-}, &args)
-
-p.MustParse(os.Args[1:])
-fmt.Println("Workers:", args.Workers)
-```
-
-```shell
-$ MYAPP_NUM_WORKERS=6 ./example
-Workers: 6
-```
-
 ### Usage strings
-
 ```go
 var args struct {
 	Input    string   `arg:"positional"`
@ -172,10 +134,10 @@ arg.MustParse(&args)

 ```shell
 $ ./example -h
-Usage: [--verbose] [--dataset DATASET] [--optimize OPTIMIZE] [--help] INPUT [OUTPUT [OUTPUT ...]]
+Usage: [--verbose] [--dataset DATASET] [--optimize OPTIMIZE] [--help] INPUT [OUTPUT [OUTPUT ...]] 

 Positional arguments:
-  INPUT
+  INPUT 
  OUTPUT

 Options:
@ -196,7 +158,20 @@ var args struct {
 arg.MustParse(&args)
 ```

-Command line arguments take precedence over environment variables, which take precedence over default values. This means that we check whether a certain option was provided on the command line, then if not, we check for an environment variable (only if an `env` tag was provided), then if none is found, we check for a `default` tag containing a default value.
+### Default values (before v1.2)
+
+```go
+var args struct {
+	Foo string
+	Bar bool
+}
+arg.Foo = "abc"
+arg.MustParse(&args)
+```
+
+### Combining command line options, environment variables, and default values
+
+You can combine command line arguments, environment variables, and default values. Command line arguments take precedence over environment variables, which take precedence over default values. This means that we check whether a certain option was provided on the command line, then if not, we check for an environment variable (only if an `env` tag was provided), then if none is found, we check for a `default` tag containing a default value.

 ```go
 var args struct {
@ -205,23 +180,7 @@ var args struct {
 arg.MustParse(&args)
 ```

-#### Ignoring environment variables and/or default values
-
-```go
-var args struct {
-    Test  string `arg:"-t,env:TEST" default:"something"`
-}
-
-p, err := arg.NewParser(arg.Config{
-    IgnoreEnv: true,
-    IgnoreDefault: true,
-}, &args)
-
-err = p.Parse(os.Args[1:])
-```
-
 ### Arguments with multiple values
-
 ```go
 var args struct {
 	Database string
@ -237,7 +196,6 @@ Fetching the following IDs from foo: [1 2 3]
 ```

 ### Arguments that can be specified multiple times, mixed with positionals
-
 ```go
 var args struct {
    Commands  []string `arg:"-c,separate"`
@ -255,7 +213,6 @@ Databases [db1 db2 db3]
 ```

 ### Arguments with keys and values
-
 ```go
 var args struct {
 	UserIDs map[string]int
@ -269,6 +226,24 @@ fmt.Println(args.UserIDs)
 map[john:123 mary:456]
 ```

+### Custom validation
+```go
+var args struct {
+	Foo string
+	Bar string
+}
+p := arg.MustParse(&args)
+if args.Foo == "" && args.Bar == "" {
+	p.Fail("you must provide either --foo or --bar")
+}
+```
+
+```shell
+./example
+Usage: samples [--foo FOO] [--bar BAR]
+error: you must provide either --foo or --bar
+```
+
 ### Version strings

 ```go
@ -291,28 +266,6 @@ $ ./example --version
 someprogram 4.3.0
 ```

-> **Note**
-> If a `--version` flag is defined in `args` or any subcommand, it overrides the built-in versioning.
-
-### Custom validation
-
-```go
-var args struct {
-	Foo string
-	Bar string
-}
-p := arg.MustParse(&args)
-if args.Foo == "" && args.Bar == "" {
-	p.Fail("you must provide either --foo or --bar")
-}
-```
-
-```shell
-./example
-Usage: samples [--foo FOO] [--bar BAR]
-error: you must provide either --foo or --bar
-```
-
 ### Overriding option names

 ```go
@ -337,11 +290,13 @@ Options:
  --help, -h             display this help and exit
 ```

+
 ### Embedded structs

 The fields of embedded structs are treated just like regular fields:

 ```go
+
 type DatabaseOptions struct {
 	Host     string
 	Username string
@ -409,7 +364,6 @@ func main() {
 	fmt.Printf("%#v\n", args.Name)
 }
 ```
-
 ```shell
 $ ./example --name=foo.bar
 main.NameDotName{Head:"foo", Tail:"bar"}
@ -446,7 +400,6 @@ func main() {
 	fmt.Printf("%#v\n", args.Name)
 }
 ```
-
 ```shell
 $ ./example --help
 Usage: test [--name NAME]
@ -461,6 +414,8 @@ main.NameDotName{Head:"file", Tail:"txt"}

 ### Custom placeholders

+*Introduced in version 1.3.0*
+
 Use the `placeholder` tag to control which placeholder text is used in the usage text.

 ```go
@ -472,7 +427,6 @@ var args struct {
 }
 arg.MustParse(&args)
 ```
-
 ```shell
 $ ./example -h
 Usage: example [--optimize LEVEL] [--maxjobs N] SRC [DST [DST ...]]
@ -490,9 +444,6 @@ Options:

 ### Description strings

-A descriptive message can be added at the top of the help text by implementing
-a `Description` function that returns a string.
-
 ```go
 type args struct {
 	Foo string
@ -518,37 +469,10 @@ Options:
  --help, -h             display this help and exit
 ```

-Similarly an epilogue can be added at the end of the help text by implementing
-the `Epilogue` function.
-
-```go
-type args struct {
-	Foo string
-}
-
-func (args) Epilogue() string {
-	return "For more information visit github.com/alexflint/go-arg"
-}
-
-func main() {
-	var args args
-	arg.MustParse(&args)
-}
-```
-
-```shell
-$ ./example -h
-Usage: example [--foo FOO]
-
-Options:
-  --foo FOO
-  --help, -h             display this help and exit
-
-For more information visit github.com/alexflint/go-arg
-```
-
 ### Subcommands

+*Introduced in version 1.1.0*
+
 Subcommands are commonly used in tools that wish to group multiple functions into a single program. An example is the `git` tool:
 ```shell
 $ git checkout [arguments specific to checking out code]
@ -609,187 +533,15 @@ if p.Subcommand() == nil {
 }
 ```

-### Custom handling of --help and --version
-
-The following reproduces the internal logic of `MustParse` for the simple case where
-you are not using subcommands or --version. This allows you to respond
-programatically to --help, and to any errors that come up.
-
-```go
-var args struct {
-	Something string
-}
-
-p, err := arg.NewParser(arg.Config{}, &args)
-if err != nil {
-	log.Fatalf("there was an error in the definition of the Go struct: %v", err)
-}
-
-err = p.Parse(os.Args[1:])
-switch {
-case err == arg.ErrHelp:  // indicates that user wrote "--help" on command line
-	p.WriteHelp(os.Stdout)
-	os.Exit(0)
-case err != nil:
-	fmt.Printf("error: %v\n", err)
-	p.WriteUsage(os.Stdout)
-	os.Exit(1)
-}
-```
-
-```shell
-$ go run ./example --help
-Usage: ./example --something SOMETHING
-
-Options:
-  --something SOMETHING
-  --help, -h             display this help and exit
-
-$ ./example --wrong
-error: unknown argument --wrong
-Usage: ./example --something SOMETHING
-
-$ ./example
-error: --something is required
-Usage: ./example --something SOMETHING
-```
-
-To also handle --version programatically, use the following:
-
-```go
-type args struct {
-	Something string
-}
-
-func (args) Version() string {
-	return "1.2.3"
-}
-
-func main() {
-	var args args
-	p, err := arg.NewParser(arg.Config{}, &args)
-	if err != nil {
-		log.Fatalf("there was an error in the definition of the Go struct: %v", err)
-	}
-
-	err = p.Parse(os.Args[1:])
-	switch {
-	case err == arg.ErrHelp: // found "--help" on command line
-		p.WriteHelp(os.Stdout)
-		os.Exit(0)
-	case err == arg.ErrVersion: // found "--version" on command line
-		fmt.Println(args.Version())
-		os.Exit(0)
-	case err != nil:
-		fmt.Printf("error: %v\n", err)
-		p.WriteUsage(os.Stdout)
-		os.Exit(1)
-	}
-
-	fmt.Printf("got %q\n", args.Something)
-}
-```
-
-```shell
-$ ./example --version
-1.2.3
-
-$ go run ./example --help
-1.2.3
-Usage: example --something SOMETHING
-
-Options:
-  --something SOMETHING
-  --help, -h             display this help and exit
-
-$ ./example --wrong
-1.2.3
-error: unknown argument --wrong
-Usage: example --something SOMETHING
-
-$ ./example
-error: --something is required
-Usage: example --something SOMETHING
-```
-
-To generate subcommand-specific help messages, use the following most general version
-(this also works in absence of subcommands but is a bit more complex):
-
-```go
-type fetchCmd struct {
-	Count int
-}
-
-type args struct {
-	Something string
-	Fetch     *fetchCmd `arg:"subcommand"`
-}
-
-func (args) Version() string {
-	return "1.2.3"
-}
-
-func main() {
-	var args args
-	p, err := arg.NewParser(arg.Config{}, &args)
-	if err != nil {
-		log.Fatalf("there was an error in the definition of the Go struct: %v", err)
-	}
-
-	err = p.Parse(os.Args[1:])
-	switch {
-	case err == arg.ErrHelp: // found "--help" on command line
-		p.WriteHelpForSubcommand(os.Stdout, p.SubcommandNames()...)
-		os.Exit(0)
-	case err == arg.ErrVersion: // found "--version" on command line
-		fmt.Println(args.Version())
-		os.Exit(0)
-	case err != nil:
-		fmt.Printf("error: %v\n", err)
-		p.WriteUsageForSubcommand(os.Stdout, p.SubcommandNames()...)
-		os.Exit(1)
-	}
-}
-```
-
-```shell
-$ ./example --version
-1.2.3
-
-$ ./example --help
-1.2.3
-Usage: example [--something SOMETHING] <command> [<args>]
-
-Options:
-  --something SOMETHING
-  --help, -h             display this help and exit
-  --version              display version and exit
-
-Commands:
-  fetch
-
-$ ./example fetch --help
-1.2.3
-Usage: example fetch [--count COUNT]
-
-Options:
-  --count COUNT
-
-Global options:
-  --something SOMETHING
-  --help, -h             display this help and exit
-  --version              display version and exit
-```
-
 ### API Documentation

-https://pkg.go.dev/github.com/alexflint/go-arg
+https://godoc.org/github.com/alexflint/go-arg

 ### Rationale

 There are many command line argument parsing libraries for Go, including one in the standard library, so why build another?

-The `flag` library that ships in the standard library seems awkward to me. Positional arguments must precede options, so `./prog x --foo=1` does what you expect but `./prog --foo=1 x` does not. It also does not allow arguments to have both long (`--foo`) and short (`-f`) forms.
+The `flag` library that ships in the standard library seems awkward to me. Positional arguments must preceed options, so `./prog x --foo=1` does what you expect but `./prog --foo=1 x` does not. It also does not allow arguments to have both long (`--foo`) and short (`-f`) forms.

 Many third-party argument parsing libraries are great for writing sophisticated command line interfaces, but feel to me like overkill for a simple script with a few flags.

@ -797,4 +549,4 @@ The idea behind `go-arg` is that Go already has an excellent way to describe dat

 ### Backward compatibility notes

-Earlier versions of this library required the help text to be part of the `arg` tag. This is still supported but is now deprecated. Instead, you should use a separate `help` tag, described above, which makes it possible to include commas inside help text.
+Earlier versions of this library required the help text to be part of the `arg` tag. This is still supported but is now deprecated. Instead, you should use a separate `help` tag, described above, which removes most of the limits on the text you can write. In particular, you will need to use the new `help` tag if your help text includes any commas.
--- a/example_test.go
+++ b/example_test.go
@ -162,8 +162,8 @@ func Example_helpText() {
 	}

 	// This is only necessary when running inside golang's runnable example harness
-	mustParseExit = func(int) {}
-	mustParseOut = os.Stdout
+	osExit = func(int) {}
+	stdout = os.Stdout

 	MustParse(&args)

@ -195,18 +195,19 @@ func Example_helpPlaceholder() {
 	}

 	// This is only necessary when running inside golang's runnable example harness
-	mustParseExit = func(int) {}
-	mustParseOut = os.Stdout
+	osExit = func(int) {}
+	stdout = os.Stdout

 	MustParse(&args)

 	// output:
+
 	// Usage: example [--optimize LEVEL] [--maxjobs N] SRC [DST [DST ...]]
-	//
+
 	// Positional arguments:
 	//   SRC
 	//   DST
-	//
+
 	// Options:
 	//   --optimize LEVEL, -O LEVEL
 	//                          optimization level
@ -235,8 +236,8 @@ func Example_helpTextWithSubcommand() {
 	}

 	// This is only necessary when running inside golang's runnable example harness
-	mustParseExit = func(int) {}
-	mustParseOut = os.Stdout
+	osExit = func(int) {}
+	stdout = os.Stdout

 	MustParse(&args)

@ -273,8 +274,8 @@ func Example_helpTextWhenUsingSubcommand() {
 	}

 	// This is only necessary when running inside golang's runnable example harness
-	mustParseExit = func(int) {}
-	mustParseOut = os.Stdout
+	osExit = func(int) {}
+	stdout = os.Stdout

 	MustParse(&args)

@ -310,9 +311,10 @@ func Example_writeHelpForSubcommand() {
 	}

 	// This is only necessary when running inside golang's runnable example harness
-	exit := func(int) {}
+	osExit = func(int) {}
+	stdout = os.Stdout

-	p, err := NewParser(Config{Exit: exit}, &args)
+	p, err := NewParser(Config{}, &args)
 	if err != nil {
 		fmt.Println(err)
 		os.Exit(1)
@ -358,9 +360,10 @@ func Example_writeHelpForSubcommandNested() {
 	}

 	// This is only necessary when running inside golang's runnable example harness
-	exit := func(int) {}
+	osExit = func(int) {}
+	stdout = os.Stdout

-	p, err := NewParser(Config{Exit: exit}, &args)
+	p, err := NewParser(Config{}, &args)
 	if err != nil {
 		fmt.Println(err)
 		os.Exit(1)
@ -394,8 +397,8 @@ func Example_errorText() {
 	}

 	// This is only necessary when running inside golang's runnable example harness
-	mustParseExit = func(int) {}
-	mustParseOut = os.Stdout
+	osExit = func(int) {}
+	stderr = os.Stdout

 	MustParse(&args)

@ -418,8 +421,8 @@ func Example_errorTextForSubcommand() {
 	}

 	// This is only necessary when running inside golang's runnable example harness
-	mustParseExit = func(int) {}
-	mustParseOut = os.Stdout
+	osExit = func(int) {}
+	stderr = os.Stdout

 	MustParse(&args)

@ -454,8 +457,8 @@ func Example_subcommand() {
 	}

 	// This is only necessary when running inside golang's runnable example harness
-	mustParseExit = func(int) {}
-	mustParseOut = os.Stdout
+	osExit = func(int) {}
+	stderr = os.Stdout

 	MustParse(&args)

@ -502,45 +505,3 @@ func Example_allSupportedTypes() {

 	// output:
 }
-
-func Example_envVarOnly() {
-	os.Args = split("./example")
-	_ = os.Setenv("AUTH_KEY", "my_key")
-
-	defer os.Unsetenv("AUTH_KEY")
-
-	var args struct {
-		AuthKey string `arg:"--,env:AUTH_KEY"`
-	}
-
-	MustParse(&args)
-
-	fmt.Println(args.AuthKey)
-	// output: my_key
-}
-
-func Example_envVarOnlyShouldIgnoreFlag() {
-	os.Args = split("./example --=my_key")
-
-	var args struct {
-		AuthKey string `arg:"--,env:AUTH_KEY"`
-	}
-
-	err := Parse(&args)
-
-	fmt.Println(err)
-	// output: unknown argument --=my_key
-}
-
-func Example_envVarOnlyShouldIgnoreShortFlag() {
-	os.Args = split("./example -=my_key")
-
-	var args struct {
-		AuthKey string `arg:"--,env:AUTH_KEY"`
-	}
-
-	err := Parse(&args)
-
-	fmt.Println(err)
-	// output: unknown argument -=my_key
-}
--- a/go.mod
+++ b/go.mod
@ -1,14 +1,8 @@
-module go.wit.com/dev/alexflint/arg
+module github.com/alexflint/go-arg

 require (
-	github.com/alexflint/go-scalar v1.2.0
+	github.com/alexflint/go-scalar v1.1.0
 	github.com/stretchr/testify v1.7.0
 )

-require (
-	github.com/davecgh/go-spew v1.1.1 // indirect
-	github.com/pmezard/go-difflib v1.0.0 // indirect
-	gopkg.in/yaml.v3 v3.0.0 // indirect
-)
-
-go 1.18
+go 1.13
--- a/go.sum
+++ b/go.sum
@ -1,5 +1,5 @@
-github.com/alexflint/go-scalar v1.2.0 h1:WR7JPKkeNpnYIOfHRa7ivM21aWAdHD0gEWHCx+WQBRw=
-github.com/alexflint/go-scalar v1.2.0/go.mod h1:LoFvNMqS1CPrMVltza4LvnGKhaSpc3oyLEBUZVhhS2o=
+github.com/alexflint/go-scalar v1.1.0 h1:aaAouLLzI9TChcPXotr6gUhq+Scr8rl0P9P4PnltbhM=
+github.com/alexflint/go-scalar v1.1.0/go.mod h1:LoFvNMqS1CPrMVltza4LvnGKhaSpc3oyLEBUZVhhS2o=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
@ -11,6 +11,5 @@ github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5Cc
 github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
-gopkg.in/yaml.v3 v3.0.0 h1:hjy8E9ON/egN1tAYqKb61G10WtihqetD4sz2H+8nIeA=
-gopkg.in/yaml.v3 v3.0.0/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
--- a/parse.go
+++ b/parse.go
@ -5,7 +5,6 @@ import (
 	"encoding/csv"
 	"errors"
 	"fmt"
-	"io"
 	"os"
 	"path/filepath"
 	"reflect"
@ -44,25 +43,23 @@ func (p path) Child(f reflect.StructField) path {

 // spec represents a command line option
 type spec struct {
-	dest          path
-	field         reflect.StructField // the struct field from which this option was created
-	long          string              // the --long form for this option, or empty if none
-	short         string              // the -s short form for this option, or empty if none
-	cardinality   cardinality         // determines how many tokens will be present (possible values: zero, one, multiple)
-	required      bool                // if true, this option must be present on the command line
-	positional    bool                // if true, this option will be looked for in the positional flags
-	separate      bool                // if true, each slice and map entry will have its own --flag
-	help          string              // the help text for this option
-	env           string              // the name of the environment variable for this option, or empty for none
-	defaultValue  reflect.Value       // default value for this option
-	defaultString string              // default value for this option, in string form to be displayed in help text
-	placeholder   string              // placeholder string in help
+	dest        path
+	field       reflect.StructField // the struct field from which this option was created
+	long        string              // the --long form for this option, or empty if none
+	short       string              // the -s short form for this option, or empty if none
+	cardinality cardinality         // determines how many tokens will be present (possible values: zero, one, multiple)
+	required    bool                // if true, this option must be present on the command line
+	positional  bool                // if true, this option will be looked for in the positional flags
+	separate    bool                // if true, each slice and map entry will have its own --flag
+	help        string              // the help text for this option
+	env         string              // the name of the environment variable for this option, or empty for none
+	defaultVal  string              // default value for this option
+	placeholder string              // name of the data in help
 }

 // command represents a named subcommand, or the top-level command
 type command struct {
 	name        string
-	aliases     []string
 	help        string
 	dest        path
 	specs       []*spec
@ -70,48 +67,33 @@ type command struct {
 	parent      *command
 }

-// ErrHelp indicates that the builtin -h or --help were provided
+// ErrHelp indicates that -h or --help were provided
 var ErrHelp = errors.New("help requested by user")

-// ErrVersion indicates that the builtin --version was provided
+// ErrVersion indicates that --version was provided
 var ErrVersion = errors.New("version requested by user")

-// for monkey patching in example and test code
-var mustParseExit = os.Exit
-var mustParseOut io.Writer = os.Stdout
-
-/*
-	This allows you to have common arg values defined in a GO package
-
-	package 'foo'
-	function init() {
-		args.Register(&argsFoo)
-	}
-*/
-
-// This stores the args sent from the GO packages
-var register []interface{}
-
-func Register(dest ...interface{}) {
-	register = append(register, dest...)
-}
-
 // MustParse processes command line arguments and exits upon failure
 func MustParse(dest ...interface{}) *Parser {
-	register = append(register, dest...)
-	return mustParse(Config{Exit: mustParseExit, Out: mustParseOut}, register...)
-}
-
-// mustParse is a helper that facilitates testing
-func mustParse(config Config, dest ...interface{}) *Parser {
-	p, err := NewParser(config, dest...)
+	p, err := NewParser(Config{}, dest...)
 	if err != nil {
-		fmt.Fprintln(config.Out, err)
-		config.Exit(2)
-		return nil
+		fmt.Fprintln(stdout, err)
+		osExit(-1)
+		return nil // just in case osExit was monkey-patched
+	}
+
+	err = p.Parse(flags())
+	switch {
+	case err == ErrHelp:
+		p.writeHelpForSubcommand(stdout, p.lastCmd)
+		osExit(0)
+	case err == ErrVersion:
+		fmt.Fprintln(stdout, p.version)
+		osExit(0)
+	case err != nil:
+		p.failWithSubcommand(err.Error(), p.lastCmd)
 	}

-	p.MustParse(flags())
 	return p
 }

@ -124,24 +106,8 @@ func Parse(dest ...interface{}) error {
 	return p.Parse(flags())
 }

-// pass in a "pretend" os.Args. Used for bash autocomplete
-func ParseFlags(flags []string, dest ...interface{}) (*Parser, error) {
-	p, err := NewParser(Config{}, dest...)
-	if err != nil {
-		return p, err
-	}
-	overrideFlags = append(overrideFlags, flags...)
-	err = p.Parse(flags)
-	return p, err
-}
-
-var overrideFlags []string
-
 // flags gets all command line arguments other than the first (program name)
 func flags() []string {
-	if len(overrideFlags) > 0 {
-		return overrideFlags
-	}
 	if len(os.Args) == 0 { // os.Args could be empty
 		return nil
 	}
@ -155,23 +121,6 @@ type Config struct {

 	// IgnoreEnv instructs the library not to read environment variables
 	IgnoreEnv bool
-
-	// IgnoreDefault instructs the library not to reset the variables to the
-	// default values, including pointers to sub commands
-	IgnoreDefault bool
-
-	// StrictSubcommands intructs the library not to allow global commands after
-	// subcommand
-	StrictSubcommands bool
-
-	// EnvPrefix instructs the library to use a name prefix when reading environment variables.
-	EnvPrefix string
-
-	// Exit is called to terminate the process with an error code (defaults to os.Exit)
-	Exit func(int)
-
-	// Out is where help text, usage text, and failure messages are printed (defaults to os.Stdout)
-	Out io.Writer
 }

 // Parser represents a set of command line options with destination values
@ -181,10 +130,9 @@ type Parser struct {
 	config      Config
 	version     string
 	description string
-	epilogue    string

 	// the following field changes during processing of command line arguments
-	subcommand []string
+	lastCmd *command
 }

 // Versioned is the interface that the destination struct should implement to
@ -203,14 +151,6 @@ type Described interface {
 	Description() string
 }

-// Epilogued is the interface that the destination struct should implement to
-// add an epilogue string at the bottom of the help message.
-type Epilogued interface {
-	// Epilogue returns the string that will be printed on a line by itself
-	// at the end of the help message.
-	Epilogue() string
-}
-
 // walkFields calls a function for each field of a struct, recursively expanding struct fields.
 func walkFields(t reflect.Type, visit func(field reflect.StructField, owner reflect.Type) bool) {
 	walkFieldsImpl(t, visit, nil)
@ -234,14 +174,6 @@ func walkFieldsImpl(t reflect.Type, visit func(field reflect.StructField, owner

 // NewParser constructs a parser from a list of destination structs
 func NewParser(config Config, dests ...interface{}) (*Parser, error) {
-	// fill in defaults
-	if config.Exit == nil {
-		config.Exit = os.Exit
-	}
-	if config.Out == nil {
-		config.Out = os.Stdout
-	}
-
 	// first pick a name for the command for use in the usage text
 	var name string
 	switch {
@ -271,36 +203,23 @@ func NewParser(config Config, dests ...interface{}) (*Parser, error) {
 			panic(fmt.Sprintf("%s is not a pointer (did you forget an ampersand?)", t))
 		}

-		cmd, err := cmdFromStruct(name, path{root: i}, t, config.EnvPrefix)
+		cmd, err := cmdFromStruct(name, path{root: i}, t)
 		if err != nil {
 			return nil, err
 		}

-		// for backwards compatibility, add nonzero field values as defaults
-		// this applies only to the top-level command, not to subcommands (this inconsistency
-		// is the reason that this method for setting default values was deprecated)
+		// add nonzero field values as defaults
 		for _, spec := range cmd.specs {
-			// get the value
-			v := p.val(spec.dest)
-
-			// if the value is the "zero value" (e.g. nil pointer, empty struct) then ignore
-			if isZero(v) {
-				continue
-			}
-
-			// store as a default
-			spec.defaultValue = v
-
-			// we need a string to display in help text
-			// if MarshalText is implemented then use that
-			if m, ok := v.Interface().(encoding.TextMarshaler); ok {
-				s, err := m.MarshalText()
-				if err != nil {
-					return nil, fmt.Errorf("%v: error marshaling default value to string: %v", spec.dest, err)
+			if v := p.val(spec.dest); v.IsValid() && !isZero(v) {
+				if defaultVal, ok := v.Interface().(encoding.TextMarshaler); ok {
+					str, err := defaultVal.MarshalText()
+					if err != nil {
+						return nil, fmt.Errorf("%v: error marshaling default value to string: %v", spec.dest, err)
+					}
+					spec.defaultVal = string(str)
+				} else {
+					spec.defaultVal = fmt.Sprintf("%v", v)
 				}
-				spec.defaultString = string(s)
-			} else {
-				spec.defaultString = fmt.Sprintf("%v", v)
 			}
 		}

@ -313,22 +232,12 @@ func NewParser(config Config, dests ...interface{}) (*Parser, error) {
 		if dest, ok := dest.(Described); ok {
 			p.description = dest.Description()
 		}
-		if dest, ok := dest.(Epilogued); ok {
-			p.epilogue = dest.Epilogue()
-		}
-	}
-
-	// Set the parent of the subcommands to be the top-level command
-	// to make sure that global options work when there is more than one
-	// dest supplied.
-	for _, subcommand := range p.cmd.subcommands {
-		subcommand.parent = p.cmd
 	}

 	return &p, nil
 }

-func cmdFromStruct(name string, dest path, t reflect.Type, envPrefix string) (*command, error) {
+func cmdFromStruct(name string, dest path, t reflect.Type) (*command, error) {
 	// commands can only be created from pointers to structs
 	if t.Kind() != reflect.Ptr {
 		return nil, fmt.Errorf("subcommands must be pointers to structs but %s is a %s",
@ -379,8 +288,13 @@ func cmdFromStruct(name string, dest path, t reflect.Type, envPrefix string) (*c
 			spec.help = help
 		}

-		// process each comma-separated part of the tag
-		var isSubcommand bool
+		defaultVal, hasDefault := field.Tag.Lookup("default")
+		if hasDefault {
+			spec.defaultVal = defaultVal
+		}
+
+		// Look at the tag
+		var isSubcommand bool // tracks whether this field is a subcommand
 		for _, key := range strings.Split(tag, ",") {
 			if key == "" {
 				continue
@ -398,13 +312,18 @@ func cmdFromStruct(name string, dest path, t reflect.Type, envPrefix string) (*c
 			case strings.HasPrefix(key, "--"):
 				spec.long = key[2:]
 			case strings.HasPrefix(key, "-"):
-				if len(key) > 2 {
+				if len(key) != 2 {
 					errs = append(errs, fmt.Sprintf("%s.%s: short arguments must be one character only",
 						t.Name(), field.Name))
 					return false
 				}
 				spec.short = key[1:]
 			case key == "required":
+				if hasDefault {
+					errs = append(errs, fmt.Sprintf("%s.%s: 'required' cannot be used when a default value is specified",
+						t.Name(), field.Name))
+					return false
+				}
 				spec.required = true
 			case key == "positional":
 				spec.positional = true
@ -415,30 +334,24 @@ func cmdFromStruct(name string, dest path, t reflect.Type, envPrefix string) (*c
 			case key == "env":
 				// Use override name if provided
 				if value != "" {
-					spec.env = envPrefix + value
+					spec.env = value
 				} else {
-					spec.env = envPrefix + strings.ToUpper(field.Name)
+					spec.env = strings.ToUpper(field.Name)
 				}
 			case key == "subcommand":
 				// decide on a name for the subcommand
-				var cmdnames []string
-				if value == "" {
-					cmdnames = []string{strings.ToLower(field.Name)}
-				} else {
-					cmdnames = strings.Split(value, "|")
-				}
-				for i := range cmdnames {
-					cmdnames[i] = strings.TrimSpace(cmdnames[i])
+				cmdname := value
+				if cmdname == "" {
+					cmdname = strings.ToLower(field.Name)
 				}

 				// parse the subcommand recursively
-				subcmd, err := cmdFromStruct(cmdnames[0], subdest, field.Type, envPrefix)
+				subcmd, err := cmdFromStruct(cmdname, subdest, field.Type)
 				if err != nil {
 					errs = append(errs, err.Error())
 					return false
 				}

-				subcmd.aliases = cmdnames[1:]
 				subcmd.parent = &cmd
 				subcmd.help = field.Tag.Get("help")

@ -450,7 +363,6 @@ func cmdFromStruct(name string, dest path, t reflect.Type, envPrefix string) (*c
 			}
 		}

-		// placeholder is the string used in the help text like this: "--somearg PLACEHOLDER"
 		placeholder, hasPlaceholder := field.Tag.Lookup("placeholder")
 		if hasPlaceholder {
 			spec.placeholder = placeholder
@ -460,60 +372,27 @@ func cmdFromStruct(name string, dest path, t reflect.Type, envPrefix string) (*c
 			spec.placeholder = strings.ToUpper(spec.field.Name)
 		}

-		// if this is a subcommand then we've done everything we need to do
-		if isSubcommand {
-			return false
-		}
-
-		// check whether this field is supported. It's good to do this here rather than
+		// Check whether this field is supported. It's good to do this here rather than
 		// wait until ParseValue because it means that a program with invalid argument
 		// fields will always fail regardless of whether the arguments it received
 		// exercised those fields.
-		var err error
-		spec.cardinality, err = cardinalityOf(field.Type)
-		if err != nil {
-			errs = append(errs, fmt.Sprintf("%s.%s: %s fields are not supported",
-				t.Name(), field.Name, field.Type.String()))
-			return false
-		}
+		if !isSubcommand {
+			cmd.specs = append(cmd.specs, &spec)

-		defaultString, hasDefault := field.Tag.Lookup("default")
-		if hasDefault {
-			// we do not support default values for maps and slices
-			if spec.cardinality == multiple {
+			var err error
+			spec.cardinality, err = cardinalityOf(field.Type)
+			if err != nil {
+				errs = append(errs, fmt.Sprintf("%s.%s: %s fields are not supported",
+					t.Name(), field.Name, field.Type.String()))
+				return false
+			}
+			if spec.cardinality == multiple && hasDefault {
 				errs = append(errs, fmt.Sprintf("%s.%s: default values are not supported for slice or map fields",
 					t.Name(), field.Name))
 				return false
 			}
-
-			// a required field cannot also have a default value
-			if spec.required {
-				errs = append(errs, fmt.Sprintf("%s.%s: 'required' cannot be used when a default value is specified",
-					t.Name(), field.Name))
-				return false
-			}
-
-			// parse the default value
-			spec.defaultString = defaultString
-			if field.Type.Kind() == reflect.Ptr {
-				// here we have a field of type *T and we create a new T, no need to dereference
-				// in order for the value to be settable
-				spec.defaultValue = reflect.New(field.Type.Elem())
-			} else {
-				// here we have a field of type T and we create a new T and then dereference it
-				// so that the resulting value is settable
-				spec.defaultValue = reflect.New(field.Type).Elem()
-			}
-			err := scalar.ParseValue(spec.defaultValue, defaultString)
-			if err != nil {
-				errs = append(errs, fmt.Sprintf("%s.%s: error processing default value: %v", t.Name(), field.Name, err))
-				return false
-			}
 		}

-		// add the spec to the list of specs
-		cmd.specs = append(cmd.specs, &spec)
-
 		// if this was an embedded field then we already returned true up above
 		return false
 	})
@ -536,15 +415,8 @@ func cmdFromStruct(name string, dest path, t reflect.Type, envPrefix string) (*c
 	return &cmd, nil
 }

-// Parse processes the given command line option, storing the results in the fields
-// of the structs from which NewParser was constructed.
-//
-// It returns ErrHelp if "--help" is one of the command line args and ErrVersion if
-// "--version" is one of the command line args (the latter only applies if the
-// destination struct passed to NewParser implements Versioned.)
-//
-// To respond to --help and --version in the way that MustParse does, see examples
-// in the README under "Custom handling of --help and --version".
+// Parse processes the given command line option, storing the results in the field
+// of the structs from which NewParser was constructed
 func (p *Parser) Parse(args []string) error {
 	err := p.process(args)
 	if err != nil {
@ -561,20 +433,6 @@ func (p *Parser) Parse(args []string) error {
 	return err
 }

-func (p *Parser) MustParse(args []string) {
-	err := p.Parse(args)
-	switch {
-	case err == ErrHelp:
-		p.WriteHelpForSubcommand(p.config.Out, p.subcommand...)
-		p.config.Exit(0)
-	case err == ErrVersion:
-		fmt.Fprintln(p.config.Out, p.version)
-		p.config.Exit(0)
-	case err != nil:
-		p.FailSubcommand(err.Error(), p.subcommand...)
-	}
-}
-
 // process environment vars for the given arguments
 func (p *Parser) captureEnvVars(specs []*spec, wasPresent map[*spec]bool) error {
 	for _, spec := range specs {
@ -628,7 +486,7 @@ func (p *Parser) process(args []string) error {

 	// union of specs for the chain of subcommands encountered so far
 	curCmd := p.cmd
-	p.subcommand = nil
+	p.lastCmd = curCmd

 	// make a copy of the specs because we will add to this list each time we expand a subcommand
 	specs := make([]*spec, len(curCmd.specs))
@ -642,15 +500,6 @@ func (p *Parser) process(args []string) error {
 		}
 	}

-	// determine if the current command has a version option spec
-	var hasVersionOption bool
-	for _, spec := range curCmd.specs {
-		if spec.long == "version" {
-			hasVersionOption = true
-			break
-		}
-	}
-
 	// process each string from the command line
 	var allpositional bool
 	var positionals []string
@ -658,7 +507,7 @@ func (p *Parser) process(args []string) error {
 	// must use explicit for loop, not range, because we manipulate i inside the loop
 	for i := 0; i < len(args); i++ {
 		arg := args[i]
-		if arg == "--" && !allpositional {
+		if arg == "--" {
 			allpositional = true
 			continue
 		}
@ -678,17 +527,10 @@ func (p *Parser) process(args []string) error {

 			// instantiate the field to point to a new struct
 			v := p.val(subcmd.dest)
-			if v.IsNil() {
-				v.Set(reflect.New(v.Type().Elem())) // we already checked that all subcommands are struct pointers
-			}
+			v.Set(reflect.New(v.Type().Elem())) // we already checked that all subcommands are struct pointers

 			// add the new options to the set of allowed options
-			if p.config.StrictSubcommands {
-				specs = make([]*spec, len(subcmd.specs))
-				copy(specs, subcmd.specs)
-			} else {
-				specs = append(specs, subcmd.specs...)
-			}
+			specs = append(specs, subcmd.specs...)

 			// capture environment vars for these new options
 			if !p.config.IgnoreEnv {
@ -699,7 +541,7 @@ func (p *Parser) process(args []string) error {
 			}

 			curCmd = subcmd
-			p.subcommand = append(p.subcommand, arg)
+			p.lastCmd = curCmd
 			continue
 		}

@ -708,9 +550,7 @@ func (p *Parser) process(args []string) error {
 		case "-h", "--help":
 			return ErrHelp
 		case "--version":
-			if !hasVersionOption && p.version != "" {
-				return ErrVersion
-			}
+			return ErrVersion
 		}

 		// check for an equals sign, as in "--foo=bar"
@ -724,7 +564,7 @@ func (p *Parser) process(args []string) error {
 		// lookup the spec for this option (note that the "specs" slice changes as
 		// we expand subcommands so it is better not to use a map)
 		spec := findOption(specs, opt)
-		if spec == nil || opt == "" {
+		if spec == nil {
 			return fmt.Errorf("unknown argument %s", arg)
 		}
 		wasPresent[spec] = true
@ -733,7 +573,7 @@ func (p *Parser) process(args []string) error {
 		if spec.cardinality == multiple {
 			var values []string
 			if value == "" {
-				for i+1 < len(args) && isValue(args[i+1], spec.field.Type, specs) && args[i+1] != "--" {
+				for i+1 < len(args) && !isFlag(args[i+1]) && args[i+1] != "--" {
 					values = append(values, args[i+1])
 					i++
 					if spec.separate {
@ -761,7 +601,7 @@ func (p *Parser) process(args []string) error {
 			if i+1 == len(args) {
 				return fmt.Errorf("missing value for %s", arg)
 			}
-			if !isValue(args[i+1], spec.field.Type, specs) {
+			if !nextIsNumeric(spec.field.Type, args[i+1]) && isFlag(args[i+1]) {
 				return fmt.Errorf("missing value for %s", arg)
 			}
 			value = args[i+1]
@ -786,13 +626,13 @@ func (p *Parser) process(args []string) error {
 		if spec.cardinality == multiple {
 			err := setSliceOrMap(p.val(spec.dest), positionals, true)
 			if err != nil {
-				return fmt.Errorf("error processing %s: %v", spec.placeholder, err)
+				return fmt.Errorf("error processing %s: %v", spec.field.Name, err)
 			}
 			positionals = nil
 		} else {
 			err := scalar.ParseValue(p.val(spec.dest), positionals[0])
 			if err != nil {
-				return fmt.Errorf("error processing %s: %v", spec.placeholder, err)
+				return fmt.Errorf("error processing %s: %v", spec.field.Name, err)
 			}
 			positionals = positionals[1:]
 		}
@ -807,56 +647,45 @@ func (p *Parser) process(args []string) error {
 			continue
 		}

-		if spec.required {
-			if spec.short == "" && spec.long == "" {
-				msg := fmt.Sprintf("environment variable %s is required", spec.env)
-				return errors.New(msg)
-			}
+		name := strings.ToLower(spec.field.Name)
+		if spec.long != "" && !spec.positional {
+			name = "--" + spec.long
+		}

-			msg := fmt.Sprintf("%s is required", spec.placeholder)
+		if spec.required {
+			msg := fmt.Sprintf("%s is required", name)
 			if spec.env != "" {
 				msg += " (or environment variable " + spec.env + ")"
 			}
-
 			return errors.New(msg)
 		}
-
-		if spec.defaultValue.IsValid() && !p.config.IgnoreDefault {
-			// One issue here is that if the user now modifies the value then
-			// the default value stored in the spec will be corrupted. There
-			// is no general way to "deep-copy" values in Go, and we still
-			// support the old-style method for specifying defaults as
-			// Go values assigned directly to the struct field, so we are stuck.
-			p.val(spec.dest).Set(spec.defaultValue)
+		if spec.defaultVal != "" {
+			err := scalar.ParseValue(p.val(spec.dest), spec.defaultVal)
+			if err != nil {
+				return fmt.Errorf("error processing default value for %s: %v", name, err)
+			}
 		}
 	}

 	return nil
 }

-// isFlag returns true if a token is a flag such as "-v" or "--user" but not "-" or "--"
-func isFlag(s string) bool {
-	return strings.HasPrefix(s, "-") && strings.TrimLeft(s, "-") != ""
-}
-
-// isValue returns true if a token should be consumed as a value for a flag of type t. This
-// is almost always the inverse of isFlag. The one exception is for negative numbers, in which
-// case we check the list of active options and return true if its not present there.
-func isValue(s string, t reflect.Type, specs []*spec) bool {
+func nextIsNumeric(t reflect.Type, s string) bool {
 	switch t.Kind() {
-	case reflect.Ptr, reflect.Slice:
-		return isValue(s, t.Elem(), specs)
+	case reflect.Ptr:
+		return nextIsNumeric(t.Elem(), s)
 	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Float32, reflect.Float64, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
 		v := reflect.New(t)
 		err := scalar.ParseValue(v, s)
-		// if value can be parsed and is not an explicit option declared elsewhere, then use it as a value
-		if err == nil && (!strings.HasPrefix(s, "-") || findOption(specs, strings.TrimPrefix(s, "-")) == nil) {
-			return true
-		}
+		return err == nil
+	default:
+		return false
 	}
+}

-	// default case that is used in all cases other than negative numbers: inverse of isFlag
-	return !isFlag(s)
+// isFlag returns true if a token is a flag such as "-v" or "--user" but not "-" or "--"
+func isFlag(s string) bool {
+	return strings.HasPrefix(s, "-") && strings.TrimLeft(s, "-") != ""
 }

 // val returns a reflect.Value corresponding to the current value for the
@ -895,11 +724,6 @@ func findSubcommand(cmds []*command, name string) *command {
 		if cmd.name == name {
 			return cmd
 		}
-		for _, alias := range cmd.aliases {
-			if alias == name {
-				return cmd
-			}
-		}
 	}
 	return nil
 }
--- a/parse_test.go
+++ b/parse_test.go
@ -2,7 +2,6 @@ package arg

 import (
 	"bytes"
-	"encoding/json"
 	"fmt"
 	"net"
 	"net/mail"
@ -28,11 +27,11 @@ func parse(cmdline string, dest interface{}) error {
 }

 func pparse(cmdline string, dest interface{}) (*Parser, error) {
-	return parseWithEnv(Config{}, cmdline, nil, dest)
+	return parseWithEnv(cmdline, nil, dest)
 }

-func parseWithEnv(config Config, cmdline string, env []string, dest interface{}) (*Parser, error) {
-	p, err := NewParser(config, dest)
+func parseWithEnv(cmdline string, env []string, dest interface{}) (*Parser, error) {
+	p, err := NewParser(Config{}, dest)
 	if err != nil {
 		return nil, err
 	}
@ -96,21 +95,6 @@ func TestInt(t *testing.T) {
 	assert.EqualValues(t, 8, *args.Ptr)
 }

-func TestHexOctBin(t *testing.T) {
-	var args struct {
-		Hex         int
-		Oct         int
-		Bin         int
-		Underscored int
-	}
-	err := parse("--hex 0xA --oct 0o10 --bin 0b101 --underscored 123_456", &args)
-	require.NoError(t, err)
-	assert.EqualValues(t, 10, args.Hex)
-	assert.EqualValues(t, 8, args.Oct)
-	assert.EqualValues(t, 5, args.Bin)
-	assert.EqualValues(t, 123456, args.Underscored)
-}
-
 func TestNegativeInt(t *testing.T) {
 	var args struct {
 		Foo int
@ -120,91 +104,17 @@ func TestNegativeInt(t *testing.T) {
 	assert.EqualValues(t, args.Foo, -100)
 }

-func TestNegativeFloat(t *testing.T) {
-	var args struct {
-		Foo float64
-	}
-	err := parse("-foo -99", &args)
-	require.NoError(t, err)
-	assert.EqualValues(t, args.Foo, -99)
-}
-
-func TestNumericFlag(t *testing.T) {
-	var args struct {
-		UseIPv6 bool `arg:"-6"`
-		Foo     int
-	}
-	err := parse("-6", &args)
-	require.NoError(t, err)
-	assert.EqualValues(t, args.UseIPv6, true)
-}
-
-func TestNumericFlagTakesPrecedence(t *testing.T) {
-	var args struct {
-		UseIPv6 bool `arg:"-6"`
-		Foo     int
-	}
-	err := parse("-foo -6", &args)
-	require.Error(t, err)
-}
-
-func TestRepeatedNegativeInts(t *testing.T) {
-	var args struct {
-		Ints []int `arg:"--numbers"`
-	}
-	err := parse("--numbers -1 -2 -6", &args)
-	require.NoError(t, err)
-	assert.EqualValues(t, args.Ints, []int{-1, -2, -6})
-}
-
-func TestRepeatedNegativeFloats(t *testing.T) {
-	var args struct {
-		Floats []float32 `arg:"--numbers"`
-	}
-	err := parse("--numbers -1 -2 -6", &args)
-	require.NoError(t, err)
-	assert.EqualValues(t, args.Floats, []float32{-1, -2, -6})
-}
-
-func TestRepeatedNegativeFloatsThenNumericFlag(t *testing.T) {
-	var args struct {
-		Floats  []float32 `arg:"--numbers"`
-		UseIPv6 bool      `arg:"-6"`
-	}
-	err := parse("--numbers -1 -2 -6", &args)
-	require.NoError(t, err)
-	assert.EqualValues(t, args.Floats, []float32{-1, -2})
-	assert.True(t, args.UseIPv6)
-}
-
-func TestRepeatedNegativeFloatsThenNonexistentFlag(t *testing.T) {
-	var args struct {
-		Floats  []float32 `arg:"--numbers"`
-		UseIPv6 bool      `arg:"-6"`
-	}
-	err := parse("--numbers -1 -2 -n", &args)
-	require.Error(t, err, "unknown argument -n")
-}
-
-func TestRepeatedNegativeIntsThenFloat(t *testing.T) {
-	var args struct {
-		Ints []int `arg:"--numbers"`
-	}
-	err := parse("--numbers -1 -2 -0.1", &args)
-	require.Error(t, err, "unknown argument -0.1")
-}
-
 func TestNegativeIntAndFloatAndTricks(t *testing.T) {
 	var args struct {
 		Foo int
 		Bar float64
 		N   int `arg:"--100"`
 	}
-	err := parse("-foo -99 -bar -60.14 -100 -101", &args)
+	err := parse("-foo -100 -bar -60.14 -100 -100", &args)
 	require.NoError(t, err)
-	assert.EqualValues(t, args.Foo, -99)
+	assert.EqualValues(t, args.Foo, -100)
 	assert.EqualValues(t, args.Bar, -60.14)
-	assert.EqualValues(t, args.N, -101)
+	assert.EqualValues(t, args.N, -100)
 }

 func TestUint(t *testing.T) {
@ -301,14 +211,6 @@ func TestRequiredWithEnv(t *testing.T) {
 	require.Error(t, err, "--foo is required (or environment variable FOO)")
 }

-func TestRequiredWithEnvOnly(t *testing.T) {
-	var args struct {
-		Foo string `arg:"required,--,-,env:FOO"`
-	}
-	_, err := parseWithEnv(Config{}, "", []string{}, &args)
-	require.Error(t, err, "environment variable FOO is required")
-}
-
 func TestShortFlag(t *testing.T) {
 	var args struct {
 		Foo string `arg:"-f"`
@ -599,6 +501,15 @@ func TestMissingValueInMiddle(t *testing.T) {
 	assert.Error(t, err)
 }

+func TestNegativeValue(t *testing.T) {
+	var args struct {
+		Foo int
+	}
+	err := parse("--foo -123", &args)
+	require.NoError(t, err)
+	assert.Equal(t, -123, args.Foo)
+}
+
 func TestInvalidInt(t *testing.T) {
 	var args struct {
 		Foo int
@ -674,15 +585,6 @@ func TestNoMoreOptionsBeforeHelp(t *testing.T) {
 	assert.NotEqual(t, ErrHelp, err)
 }

-func TestNoMoreOptionsTwice(t *testing.T) {
-	var args struct {
-		X []string `arg:"positional"`
-	}
-	err := parse("-- --", &args)
-	require.NoError(t, err)
-	assert.Equal(t, []string{"--"}, args.X)
-}
-
 func TestHelpFlag(t *testing.T) {
 	var args struct {
 		Foo string
@ -766,26 +668,11 @@ func TestMustParse(t *testing.T) {
 	assert.NotNil(t, parser)
 }

-func TestMustParseError(t *testing.T) {
-	var args struct {
-		Foo []string `default:""`
-	}
-	var exitCode int
-	var stdout bytes.Buffer
-	mustParseExit = func(code int) { exitCode = code }
-	mustParseOut = &stdout
-	os.Args = []string{"example"}
-	parser := MustParse(&args)
-	assert.Nil(t, parser)
-	assert.Equal(t, 2, exitCode)
-	assert.Contains(t, stdout.String(), "default values are not supported for slice or map fields")
-}
-
 func TestEnvironmentVariable(t *testing.T) {
 	var args struct {
 		Foo string `arg:"env"`
 	}
-	_, err := parseWithEnv(Config{}, "", []string{"FOO=bar"}, &args)
+	_, err := parseWithEnv("", []string{"FOO=bar"}, &args)
 	require.NoError(t, err)
 	assert.Equal(t, "bar", args.Foo)
 }
@ -794,7 +681,7 @@ func TestEnvironmentVariableNotPresent(t *testing.T) {
 	var args struct {
 		NotPresent string `arg:"env"`
 	}
-	_, err := parseWithEnv(Config{}, "", nil, &args)
+	_, err := parseWithEnv("", nil, &args)
 	require.NoError(t, err)
 	assert.Equal(t, "", args.NotPresent)
 }
@ -803,7 +690,7 @@ func TestEnvironmentVariableOverrideName(t *testing.T) {
 	var args struct {
 		Foo string `arg:"env:BAZ"`
 	}
-	_, err := parseWithEnv(Config{}, "", []string{"BAZ=bar"}, &args)
+	_, err := parseWithEnv("", []string{"BAZ=bar"}, &args)
 	require.NoError(t, err)
 	assert.Equal(t, "bar", args.Foo)
 }
@ -812,7 +699,7 @@ func TestEnvironmentVariableOverrideArgument(t *testing.T) {
 	var args struct {
 		Foo string `arg:"env"`
 	}
-	_, err := parseWithEnv(Config{}, "--foo zzz", []string{"FOO=bar"}, &args)
+	_, err := parseWithEnv("--foo zzz", []string{"FOO=bar"}, &args)
 	require.NoError(t, err)
 	assert.Equal(t, "zzz", args.Foo)
 }
@ -821,7 +708,7 @@ func TestEnvironmentVariableError(t *testing.T) {
 	var args struct {
 		Foo int `arg:"env"`
 	}
-	_, err := parseWithEnv(Config{}, "", []string{"FOO=bar"}, &args)
+	_, err := parseWithEnv("", []string{"FOO=bar"}, &args)
 	assert.Error(t, err)
 }

@ -829,7 +716,7 @@ func TestEnvironmentVariableRequired(t *testing.T) {
 	var args struct {
 		Foo string `arg:"env,required"`
 	}
-	_, err := parseWithEnv(Config{}, "", []string{"FOO=bar"}, &args)
+	_, err := parseWithEnv("", []string{"FOO=bar"}, &args)
 	require.NoError(t, err)
 	assert.Equal(t, "bar", args.Foo)
 }
@ -838,7 +725,7 @@ func TestEnvironmentVariableSliceArgumentString(t *testing.T) {
 	var args struct {
 		Foo []string `arg:"env"`
 	}
-	_, err := parseWithEnv(Config{}, "", []string{`FOO=bar,"baz, qux"`}, &args)
+	_, err := parseWithEnv("", []string{`FOO=bar,"baz, qux"`}, &args)
 	require.NoError(t, err)
 	assert.Equal(t, []string{"bar", "baz, qux"}, args.Foo)
 }
@ -847,7 +734,7 @@ func TestEnvironmentVariableSliceEmpty(t *testing.T) {
 	var args struct {
 		Foo []string `arg:"env"`
 	}
-	_, err := parseWithEnv(Config{}, "", []string{`FOO=`}, &args)
+	_, err := parseWithEnv("", []string{`FOO=`}, &args)
 	require.NoError(t, err)
 	assert.Len(t, args.Foo, 0)
 }
@ -856,7 +743,7 @@ func TestEnvironmentVariableSliceArgumentInteger(t *testing.T) {
 	var args struct {
 		Foo []int `arg:"env"`
 	}
-	_, err := parseWithEnv(Config{}, "", []string{`FOO=1,99`}, &args)
+	_, err := parseWithEnv("", []string{`FOO=1,99`}, &args)
 	require.NoError(t, err)
 	assert.Equal(t, []int{1, 99}, args.Foo)
 }
@ -865,7 +752,7 @@ func TestEnvironmentVariableSliceArgumentFloat(t *testing.T) {
 	var args struct {
 		Foo []float32 `arg:"env"`
 	}
-	_, err := parseWithEnv(Config{}, "", []string{`FOO=1.1,99.9`}, &args)
+	_, err := parseWithEnv("", []string{`FOO=1.1,99.9`}, &args)
 	require.NoError(t, err)
 	assert.Equal(t, []float32{1.1, 99.9}, args.Foo)
 }
@ -874,7 +761,7 @@ func TestEnvironmentVariableSliceArgumentBool(t *testing.T) {
 	var args struct {
 		Foo []bool `arg:"env"`
 	}
-	_, err := parseWithEnv(Config{}, "", []string{`FOO=true,false,0,1`}, &args)
+	_, err := parseWithEnv("", []string{`FOO=true,false,0,1`}, &args)
 	require.NoError(t, err)
 	assert.Equal(t, []bool{true, false, false, true}, args.Foo)
 }
@ -883,7 +770,7 @@ func TestEnvironmentVariableSliceArgumentWrongCsv(t *testing.T) {
 	var args struct {
 		Foo []int `arg:"env"`
 	}
-	_, err := parseWithEnv(Config{}, "", []string{`FOO=1,99\"`}, &args)
+	_, err := parseWithEnv("", []string{`FOO=1,99\"`}, &args)
 	assert.Error(t, err)
 }

@ -891,7 +778,7 @@ func TestEnvironmentVariableSliceArgumentWrongType(t *testing.T) {
 	var args struct {
 		Foo []bool `arg:"env"`
 	}
-	_, err := parseWithEnv(Config{}, "", []string{`FOO=one,two`}, &args)
+	_, err := parseWithEnv("", []string{`FOO=one,two`}, &args)
 	assert.Error(t, err)
 }

@ -899,7 +786,7 @@ func TestEnvironmentVariableMap(t *testing.T) {
 	var args struct {
 		Foo map[int]string `arg:"env"`
 	}
-	_, err := parseWithEnv(Config{}, "", []string{`FOO=1=one,99=ninetynine`}, &args)
+	_, err := parseWithEnv("", []string{`FOO=1=one,99=ninetynine`}, &args)
 	require.NoError(t, err)
 	assert.Len(t, args.Foo, 2)
 	assert.Equal(t, "one", args.Foo[1])
@ -910,21 +797,11 @@ func TestEnvironmentVariableEmptyMap(t *testing.T) {
 	var args struct {
 		Foo map[int]string `arg:"env"`
 	}
-	_, err := parseWithEnv(Config{}, "", []string{`FOO=`}, &args)
+	_, err := parseWithEnv("", []string{`FOO=`}, &args)
 	require.NoError(t, err)
 	assert.Len(t, args.Foo, 0)
 }

-func TestEnvironmentVariableWithPrefix(t *testing.T) {
-	var args struct {
-		Foo string `arg:"env"`
-	}
-
-	_, err := parseWithEnv(Config{EnvPrefix: "MYAPP_"}, "", []string{"MYAPP_FOO=bar"}, &args)
-	require.NoError(t, err)
-	assert.Equal(t, "bar", args.Foo)
-}
-
 func TestEnvironmentVariableIgnored(t *testing.T) {
 	var args struct {
 		Foo string `arg:"env"`
@ -939,37 +816,6 @@ func TestEnvironmentVariableIgnored(t *testing.T) {
 	assert.Equal(t, "", args.Foo)
 }

-func TestDefaultValuesIgnored(t *testing.T) {
-	var args struct {
-		Foo string `default:"bad"`
-	}
-
-	p, err := NewParser(Config{IgnoreDefault: true}, &args)
-	require.NoError(t, err)
-
-	err = p.Parse(nil)
-	assert.NoError(t, err)
-	assert.Equal(t, "", args.Foo)
-}
-
-func TestRequiredEnvironmentOnlyVariableIsMissing(t *testing.T) {
-	var args struct {
-		Foo string `arg:"required,--,env:FOO"`
-	}
-
-	_, err := parseWithEnv(Config{}, "", []string{""}, &args)
-	assert.Error(t, err)
-}
-
-func TestOptionalEnvironmentOnlyVariable(t *testing.T) {
-	var args struct {
-		Foo string `arg:"env:FOO"`
-	}
-
-	_, err := parseWithEnv(Config{}, "", []string{}, &args)
-	assert.NoError(t, err)
-}
-
 func TestEnvironmentVariableInSubcommandIgnored(t *testing.T) {
 	var args struct {
 		Sub *struct {
@ -982,51 +828,10 @@ func TestEnvironmentVariableInSubcommandIgnored(t *testing.T) {
 	require.NoError(t, err)

 	err = p.Parse([]string{"sub"})
-	require.NoError(t, err)
-	require.NotNil(t, args.Sub)
+	assert.NoError(t, err)
 	assert.Equal(t, "", args.Sub.Foo)
 }

-func TestParserMustParseEmptyArgs(t *testing.T) {
-	// this mirrors TestEmptyArgs
-	p, err := NewParser(Config{}, &struct{}{})
-	require.NoError(t, err)
-	assert.NotNil(t, p)
-	p.MustParse(nil)
-}
-
-func TestParserMustParse(t *testing.T) {
-	tests := []struct {
-		name    string
-		args    versioned
-		cmdLine []string
-		code    int
-		output  string
-	}{
-		{name: "help", args: struct{}{}, cmdLine: []string{"--help"}, code: 0, output: "display this help and exit"},
-		{name: "version", args: versioned{}, cmdLine: []string{"--version"}, code: 0, output: "example 3.2.1"},
-		{name: "invalid", args: struct{}{}, cmdLine: []string{"invalid"}, code: 2, output: ""},
-	}
-
-	for _, tt := range tests {
-		tt := tt
-		t.Run(tt.name, func(t *testing.T) {
-			var exitCode int
-			var stdout bytes.Buffer
-			exit := func(code int) { exitCode = code }
-
-			p, err := NewParser(Config{Exit: exit, Out: &stdout}, &tt.args)
-			require.NoError(t, err)
-			assert.NotNil(t, p)
-
-			p.MustParse(tt.cmdLine)
-			assert.NotNil(t, exitCode)
-			assert.Equal(t, tt.code, exitCode)
-			assert.Contains(t, stdout.String(), tt.output)
-		})
-	}
-}
-
 type textUnmarshaler struct {
 	val int
 }
@ -1480,55 +1285,11 @@ func TestReuseParser(t *testing.T) {
 	assert.Error(t, err)
 }

-func TestNoVersion(t *testing.T) {
+func TestVersion(t *testing.T) {
 	var args struct{}
-
-	p, err := NewParser(Config{}, &args)
-	require.NoError(t, err)
-
-	err = p.Parse([]string{"--version"})
-	assert.Error(t, err)
-	assert.NotEqual(t, ErrVersion, err)
-}
-
-func TestBuiltinVersion(t *testing.T) {
-	var args struct{}
-
-	p, err := NewParser(Config{}, &args)
-	require.NoError(t, err)
-
-	p.version = "example 3.2.1"
-
-	err = p.Parse([]string{"--version"})
+	err := parse("--version", &args)
 	assert.Equal(t, ErrVersion, err)
-}

-func TestArgsVersion(t *testing.T) {
-	var args struct {
-		Version bool `arg:"--version"`
-	}
-
-	p, err := NewParser(Config{}, &args)
-	require.NoError(t, err)
-
-	err = p.Parse([]string{"--version"})
-	require.NoError(t, err)
-	require.Equal(t, args.Version, true)
-}
-
-func TestArgsAndBuiltinVersion(t *testing.T) {
-	var args struct {
-		Version bool `arg:"--version"`
-	}
-
-	p, err := NewParser(Config{}, &args)
-	require.NoError(t, err)
-
-	p.version = "example 3.2.1"
-
-	err = p.Parse([]string{"--version"})
-	require.NoError(t, err)
-	require.Equal(t, args.Version, true)
 }

 func TestMultipleTerminates(t *testing.T) {
@ -1559,21 +1320,13 @@ func TestDefaultOptionValues(t *testing.T) {
 	require.NoError(t, err)

 	assert.Equal(t, 123, args.A)
-	if assert.NotNil(t, args.B) {
-		assert.Equal(t, 123, *args.B)
-	}
+	assert.Equal(t, 123, *args.B)
 	assert.Equal(t, "xyz", args.C)
-	if assert.NotNil(t, args.D) {
-		assert.Equal(t, "abc", *args.D)
-	}
+	assert.Equal(t, "abc", *args.D)
 	assert.Equal(t, 4.56, args.E)
-	if assert.NotNil(t, args.F) {
-		assert.Equal(t, 1.23, *args.F)
-	}
+	assert.Equal(t, 1.23, *args.F)
+	assert.True(t, args.G)
 	assert.True(t, args.G)
-	if assert.NotNil(t, args.H) {
-		assert.True(t, *args.H)
-	}
 }

 func TestDefaultUnparseable(t *testing.T) {
@ -1582,7 +1335,7 @@ func TestDefaultUnparseable(t *testing.T) {
 	}

 	err := parse("", &args)
-	assert.EqualError(t, err, `.A: error processing default value: strconv.ParseInt: parsing "x": invalid syntax`)
+	assert.EqualError(t, err, `error processing default value for --a: strconv.ParseInt: parsing "x": invalid syntax`)
 }

 func TestDefaultPositionalValues(t *testing.T) {
@ -1601,21 +1354,13 @@ func TestDefaultPositionalValues(t *testing.T) {
 	require.NoError(t, err)

 	assert.Equal(t, 456, args.A)
-	if assert.NotNil(t, args.B) {
-		assert.Equal(t, 789, *args.B)
-	}
+	assert.Equal(t, 789, *args.B)
 	assert.Equal(t, "abc", args.C)
-	if assert.NotNil(t, args.D) {
-		assert.Equal(t, "abc", *args.D)
-	}
+	assert.Equal(t, "abc", *args.D)
 	assert.Equal(t, 1.23, args.E)
-	if assert.NotNil(t, args.F) {
-		assert.Equal(t, 1.23, *args.F)
-	}
+	assert.Equal(t, 1.23, *args.F)
+	assert.True(t, args.G)
 	assert.True(t, args.G)
-	if assert.NotNil(t, args.H) {
-		assert.True(t, *args.H)
-	}
 }

 func TestDefaultValuesNotAllowedWithRequired(t *testing.T) {
@ -1629,7 +1374,7 @@ func TestDefaultValuesNotAllowedWithRequired(t *testing.T) {

 func TestDefaultValuesNotAllowedWithSlice(t *testing.T) {
 	var args struct {
-		A []int `default:"invalid"` // default values not allowed with slices
+		A []int `default:"123"` // required not allowed with default!
 	}

 	err := parse("", &args)
@ -1646,201 +1391,68 @@ func TestUnexportedFieldsSkipped(t *testing.T) {
 }

 func TestMustParseInvalidParser(t *testing.T) {
+	originalExit := osExit
+	originalStdout := stdout
+	defer func() {
+		osExit = originalExit
+		stdout = originalStdout
+	}()
+
 	var exitCode int
-	var stdout bytes.Buffer
-	exit := func(code int) { exitCode = code }
+	osExit = func(code int) { exitCode = code }
+	stdout = &bytes.Buffer{}

 	var args struct {
 		CannotParse struct{}
 	}
-	parser := mustParse(Config{Out: &stdout, Exit: exit}, &args)
+	parser := MustParse(&args)
 	assert.Nil(t, parser)
-	assert.Equal(t, 2, exitCode)
+	assert.Equal(t, -1, exitCode)
 }

 func TestMustParsePrintsHelp(t *testing.T) {
+	originalExit := osExit
+	originalStdout := stdout
 	originalArgs := os.Args
 	defer func() {
+		osExit = originalExit
+		stdout = originalStdout
 		os.Args = originalArgs
 	}()

+	var exitCode *int
+	osExit = func(code int) { exitCode = &code }
 	os.Args = []string{"someprogram", "--help"}
-
-	var exitCode int
-	var stdout bytes.Buffer
-	exit := func(code int) { exitCode = code }
+	stdout = &bytes.Buffer{}

 	var args struct{}
-	parser := mustParse(Config{Out: &stdout, Exit: exit}, &args)
+	parser := MustParse(&args)
 	assert.NotNil(t, parser)
-	assert.Equal(t, 0, exitCode)
+	require.NotNil(t, exitCode)
+	assert.Equal(t, 0, *exitCode)
 }

 func TestMustParsePrintsVersion(t *testing.T) {
+	originalExit := osExit
+	originalStdout := stdout
 	originalArgs := os.Args
 	defer func() {
+		osExit = originalExit
+		stdout = originalStdout
 		os.Args = originalArgs
 	}()

-	var exitCode int
-	var stdout bytes.Buffer
-	exit := func(code int) { exitCode = code }
-
+	var exitCode *int
+	osExit = func(code int) { exitCode = &code }
 	os.Args = []string{"someprogram", "--version"}

+	var b bytes.Buffer
+	stdout = &b
+
 	var args versioned
-	parser := mustParse(Config{Out: &stdout, Exit: exit}, &args)
+	parser := MustParse(&args)
 	require.NotNil(t, parser)
-	assert.Equal(t, 0, exitCode)
-	assert.Equal(t, "example 3.2.1\n", stdout.String())
-}
-
-type mapWithUnmarshalText struct {
-	val map[string]string
-}
-
-func (v *mapWithUnmarshalText) UnmarshalText(data []byte) error {
-	return json.Unmarshal(data, &v.val)
-}
-
-func TestTextUnmarshalerEmpty(t *testing.T) {
-	// based on https://github.com/alexflint/go-arg/issues/184
-	var args struct {
-		Config mapWithUnmarshalText `arg:"--config"`
-	}
-
-	err := parse("", &args)
-	require.NoError(t, err)
-	assert.Empty(t, args.Config)
-}
-
-func TestTextUnmarshalerEmptyPointer(t *testing.T) {
-	// a slight variant on https://github.com/alexflint/go-arg/issues/184
-	var args struct {
-		Config *mapWithUnmarshalText `arg:"--config"`
-	}
-
-	err := parse("", &args)
-	require.NoError(t, err)
-	assert.Nil(t, args.Config)
-}
-
-// similar to the above but also implements MarshalText
-type mapWithMarshalText struct {
-	val map[string]string
-}
-
-func (v *mapWithMarshalText) MarshalText(data []byte) error {
-	return json.Unmarshal(data, &v.val)
-}
-
-func (v *mapWithMarshalText) UnmarshalText(data []byte) error {
-	return json.Unmarshal(data, &v.val)
-}
-
-func TestTextMarshalerUnmarshalerEmpty(t *testing.T) {
-	// based on https://github.com/alexflint/go-arg/issues/184
-	var args struct {
-		Config mapWithMarshalText `arg:"--config"`
-	}
-
-	err := parse("", &args)
-	require.NoError(t, err)
-	assert.Empty(t, args.Config)
-}
-
-func TestTextMarshalerUnmarshalerEmptyPointer(t *testing.T) {
-	// a slight variant on https://github.com/alexflint/go-arg/issues/184
-	var args struct {
-		Config *mapWithMarshalText `arg:"--config"`
-	}
-
-	err := parse("", &args)
-	require.NoError(t, err)
-	assert.Nil(t, args.Config)
-}
-
-func TestSubcommandGlobalFlag_Before(t *testing.T) {
-	var args struct {
-		Global bool `arg:"-g"`
-		Sub    *struct {
-		} `arg:"subcommand"`
-	}
-
-	p, err := NewParser(Config{StrictSubcommands: false}, &args)
-	require.NoError(t, err)
-
-	err = p.Parse([]string{"-g", "sub"})
-	assert.NoError(t, err)
-	assert.True(t, args.Global)
-}
-
-func TestSubcommandGlobalFlag_InCommand(t *testing.T) {
-	var args struct {
-		Global bool `arg:"-g"`
-		Sub    *struct {
-		} `arg:"subcommand"`
-	}
-
-	p, err := NewParser(Config{StrictSubcommands: false}, &args)
-	require.NoError(t, err)
-
-	err = p.Parse([]string{"sub", "-g"})
-	assert.NoError(t, err)
-	assert.True(t, args.Global)
-}
-
-func TestSubcommandGlobalFlag_Before_Strict(t *testing.T) {
-	var args struct {
-		Global bool `arg:"-g"`
-		Sub    *struct {
-		} `arg:"subcommand"`
-	}
-
-	p, err := NewParser(Config{StrictSubcommands: true}, &args)
-	require.NoError(t, err)
-
-	err = p.Parse([]string{"-g", "sub"})
-	assert.NoError(t, err)
-	assert.True(t, args.Global)
-}
-
-func TestSubcommandGlobalFlag_InCommand_Strict(t *testing.T) {
-	var args struct {
-		Global bool `arg:"-g"`
-		Sub    *struct {
-		} `arg:"subcommand"`
-	}
-
-	p, err := NewParser(Config{StrictSubcommands: true}, &args)
-	require.NoError(t, err)
-
-	err = p.Parse([]string{"sub", "-g"})
-	assert.Error(t, err)
-}
-
-func TestSubcommandGlobalFlag_InCommand_Strict_Inner(t *testing.T) {
-	var args struct {
-		Global bool `arg:"-g"`
-		Sub    *struct {
-			Guard bool `arg:"-g"`
-		} `arg:"subcommand"`
-	}
-
-	p, err := NewParser(Config{StrictSubcommands: true}, &args)
-	require.NoError(t, err)
-
-	err = p.Parse([]string{"sub", "-g"})
-	require.NoError(t, err)
-	assert.False(t, args.Global)
-	require.NotNil(t, args.Sub)
-	assert.True(t, args.Sub.Guard)
-}
-
-func TestExitFunctionAndOutStreamGetFilledIn(t *testing.T) {
-	var args struct{}
-	p, err := NewParser(Config{}, &args)
-	require.NoError(t, err)
-	assert.NotNil(t, p.config.Exit) // go prohibits function pointer comparison
-	assert.Equal(t, p.config.Out, os.Stdout)
+	require.NotNil(t, exitCode)
+	assert.Equal(t, 0, *exitCode)
+	assert.Equal(t, "example 3.2.1\n", b.String())
 }
--- a/reflect.go
+++ b/reflect.go
@ -13,9 +13,9 @@ import (
 var textUnmarshalerType = reflect.TypeOf([]encoding.TextUnmarshaler{}).Elem()

 // cardinality tracks how many tokens are expected for a given spec
-//   - zero is a boolean, which does to expect any value
-//   - one is an ordinary option that will be parsed from a single token
-//   - multiple is a slice or map that can accept zero or more tokens
+//  - zero is a boolean, which does to expect any value
+//  - one is an ordinary option that will be parsed from a single token
+//  - multiple is a slice or map that can accept zero or more tokens
 type cardinality int

 const (
@ -74,10 +74,10 @@ func cardinalityOf(t reflect.Type) (cardinality, error) {
 	}
 }

-// isBoolean returns true if the type is a boolean or a pointer to a boolean
+// isBoolean returns true if the type can be parsed from a single string
 func isBoolean(t reflect.Type) bool {
 	switch {
-	case isTextUnmarshaler(t):
+	case t.Implements(textUnmarshalerType):
 		return false
 	case t.Kind() == reflect.Bool:
 		return true
@ -88,11 +88,6 @@ func isBoolean(t reflect.Type) bool {
 	}
 }

-// isTextUnmarshaler returns true if the type or its pointer implements encoding.TextUnmarshaler
-func isTextUnmarshaler(t reflect.Type) bool {
-	return t.Implements(textUnmarshalerType) || reflect.PtrTo(t).Implements(textUnmarshalerType)
-}
-
 // isExported returns true if the struct field name is exported
 func isExported(field string) bool {
 	r, _ := utf8.DecodeRuneInString(field) // returns RuneError for empty string or invalid UTF8
@ -102,7 +97,7 @@ func isExported(field string) bool {
 // isZero returns true if v contains the zero value for its type
 func isZero(v reflect.Value) bool {
 	t := v.Type()
-	if t.Kind() == reflect.Ptr || t.Kind() == reflect.Slice || t.Kind() == reflect.Map || t.Kind() == reflect.Chan || t.Kind() == reflect.Interface {
+	if t.Kind() == reflect.Slice || t.Kind() == reflect.Map {
 		return v.IsNil()
 	}
 	if !t.Comparable() {
--- a/subcommand.go
+++ b/subcommand.go
@ -1,7 +1,5 @@
 package arg

-import "fmt"
-
 // Subcommand returns the user struct for the subcommand selected by
 // the command line arguments most recently processed by the parser.
 // The return value is always a pointer to a struct. If no subcommand
@ -9,35 +7,31 @@ import "fmt"
 // no command line arguments have been processed by this parser then it
 // returns nil.
 func (p *Parser) Subcommand() interface{} {
-	if len(p.subcommand) == 0 {
+	if p.lastCmd == nil || p.lastCmd.parent == nil {
 		return nil
 	}
-	cmd, err := p.lookupCommand(p.subcommand...)
-	if err != nil {
-		return nil
-	}
-	return p.val(cmd.dest).Interface()
+	return p.val(p.lastCmd.dest).Interface()
 }

 // SubcommandNames returns the sequence of subcommands specified by the
 // user. If no subcommands were given then it returns an empty slice.
 func (p *Parser) SubcommandNames() []string {
-	return p.subcommand
-}
-
-// lookupCommand finds a subcommand based on a sequence of subcommand names. The
-// first string should be a top-level subcommand, the next should be a child
-// subcommand of that subcommand, and so on. If no strings are given then the
-// root command is returned. If no such subcommand exists then an error is
-// returned.
-func (p *Parser) lookupCommand(path ...string) (*command, error) {
-	cmd := p.cmd
-	for _, name := range path {
-		found := findSubcommand(cmd.subcommands, name)
-		if found == nil {
-			return nil, fmt.Errorf("%q is not a subcommand of %s", name, cmd.name)
-		}
-		cmd = found
+	if p.lastCmd == nil {
+		return nil
 	}
-	return cmd, nil
+
+	// make a list of ancestor commands
+	var ancestors []string
+	cur := p.lastCmd
+	for cur.parent != nil { // we want to exclude the root
+		ancestors = append(ancestors, cur.name)
+		cur = cur.parent
+	}
+
+	// reverse the list
+	out := make([]string, len(ancestors))
+	for i := 0; i < len(ancestors); i++ {
+		out[i] = ancestors[len(ancestors)-i-1]
+	}
+	return out
 }
--- a/subcommand_test.go
+++ b/subcommand_test.go
@ -83,19 +83,6 @@ func TestNamedSubcommand(t *testing.T) {
 	assert.Equal(t, []string{"ls"}, p.SubcommandNames())
 }

-func TestSubcommandAliases(t *testing.T) {
-	type listCmd struct {
-	}
-	var args struct {
-		List *listCmd `arg:"subcommand:list|ls"`
-	}
-	p, err := pparse("ls", &args)
-	require.NoError(t, err)
-	assert.NotNil(t, args.List)
-	assert.Equal(t, args.List, p.Subcommand())
-	assert.Equal(t, []string{"ls"}, p.SubcommandNames())
-}
-
 func TestEmptySubcommand(t *testing.T) {
 	type listCmd struct {
 	}
@ -126,23 +113,6 @@ func TestTwoSubcommands(t *testing.T) {
 	assert.Equal(t, []string{"list"}, p.SubcommandNames())
 }

-func TestTwoSubcommandsWithAliases(t *testing.T) {
-	type getCmd struct {
-	}
-	type listCmd struct {
-	}
-	var args struct {
-		Get  *getCmd  `arg:"subcommand:get|g"`
-		List *listCmd `arg:"subcommand:list|ls"`
-	}
-	p, err := pparse("ls", &args)
-	require.NoError(t, err)
-	assert.Nil(t, args.Get)
-	assert.NotNil(t, args.List)
-	assert.Equal(t, args.List, p.Subcommand())
-	assert.Equal(t, []string{"ls"}, p.SubcommandNames())
-}
-
 func TestSubcommandsWithOptions(t *testing.T) {
 	type getCmd struct {
 		Name string
@ -305,60 +275,6 @@ func TestNestedSubcommands(t *testing.T) {
 	}
 }

-func TestNestedSubcommandsWithAliases(t *testing.T) {
-	type child struct{}
-	type parent struct {
-		Child *child `arg:"subcommand:child|ch"`
-	}
-	type grandparent struct {
-		Parent *parent `arg:"subcommand:parent|pa"`
-	}
-	type root struct {
-		Grandparent *grandparent `arg:"subcommand:grandparent|gp"`
-	}
-
-	{
-		var args root
-		p, err := pparse("gp parent child", &args)
-		require.NoError(t, err)
-		require.NotNil(t, args.Grandparent)
-		require.NotNil(t, args.Grandparent.Parent)
-		require.NotNil(t, args.Grandparent.Parent.Child)
-		assert.Equal(t, args.Grandparent.Parent.Child, p.Subcommand())
-		assert.Equal(t, []string{"gp", "parent", "child"}, p.SubcommandNames())
-	}
-
-	{
-		var args root
-		p, err := pparse("grandparent pa", &args)
-		require.NoError(t, err)
-		require.NotNil(t, args.Grandparent)
-		require.NotNil(t, args.Grandparent.Parent)
-		require.Nil(t, args.Grandparent.Parent.Child)
-		assert.Equal(t, args.Grandparent.Parent, p.Subcommand())
-		assert.Equal(t, []string{"grandparent", "pa"}, p.SubcommandNames())
-	}
-
-	{
-		var args root
-		p, err := pparse("grandparent", &args)
-		require.NoError(t, err)
-		require.NotNil(t, args.Grandparent)
-		require.Nil(t, args.Grandparent.Parent)
-		assert.Equal(t, args.Grandparent, p.Subcommand())
-		assert.Equal(t, []string{"grandparent"}, p.SubcommandNames())
-	}
-
-	{
-		var args root
-		p, err := pparse("", &args)
-		require.NoError(t, err)
-		require.Nil(t, args.Grandparent)
-		assert.Nil(t, p.Subcommand())
-		assert.Empty(t, p.SubcommandNames())
-	}
-}
-
 func TestSubcommandsWithPositionals(t *testing.T) {
 	type listCmd struct {
 		Pattern string `arg:"positional"`
@ -495,14 +411,3 @@ func TestValForNilStruct(t *testing.T) {
 	v := p.val(path{fields: []reflect.StructField{subField, subField}})
 	assert.False(t, v.IsValid())
 }
-
-func TestSubcommandInvalidInternal(t *testing.T) {
-	// this situation should never arise in practice but still good to test for it
-	var cmd struct{}
-	p, err := NewParser(Config{}, &cmd)
-	require.NoError(t, err)
-
-	p.subcommand = []string{"should", "never", "happen"}
-	sub := p.Subcommand()
-	assert.Nil(t, sub)
-}
--- a/usage.go
+++ b/usage.go
@ -3,37 +3,54 @@ package arg
 import (
 	"fmt"
 	"io"
+	"os"
 	"strings"
 )

 // the width of the left column
 const colWidth = 25

-// Fail prints usage information to p.Config.Out and exits with status code 2.
+// to allow monkey patching in tests
+var (
+	stdout io.Writer = os.Stdout
+	stderr io.Writer = os.Stderr
+	osExit           = os.Exit
+)
+
+// Fail prints usage information to stderr and exits with non-zero status
 func (p *Parser) Fail(msg string) {
-	p.FailSubcommand(msg)
+	p.failWithSubcommand(msg, p.cmd)
 }

-// FailSubcommand prints usage information for a specified subcommand to p.Config.Out,
-// then exits with status code 2. To write usage information for a top-level
+// FailSubcommand prints usage information for a specified subcommand to stderr,
+// then exits with non-zero status. To write usage information for a top-level
 // subcommand, provide just the name of that subcommand. To write usage
 // information for a subcommand that is nested under another subcommand, provide
 // a sequence of subcommand names starting with the top-level subcommand and so
 // on down the tree.
 func (p *Parser) FailSubcommand(msg string, subcommand ...string) error {
-	err := p.WriteUsageForSubcommand(p.config.Out, subcommand...)
+	cmd, err := p.lookupCommand(subcommand...)
 	if err != nil {
 		return err
 	}
-
-	fmt.Fprintln(p.config.Out, "error:", msg)
-	p.config.Exit(2)
+	p.failWithSubcommand(msg, cmd)
 	return nil
 }

+// failWithSubcommand prints usage information for the given subcommand to stderr and exits with non-zero status
+func (p *Parser) failWithSubcommand(msg string, cmd *command) {
+	p.writeUsageForSubcommand(stderr, cmd)
+	fmt.Fprintln(stderr, "error:", msg)
+	osExit(-1)
+}
+
 // WriteUsage writes usage information to the given writer
 func (p *Parser) WriteUsage(w io.Writer) {
-	p.WriteUsageForSubcommand(w, p.subcommand...)
+	cmd := p.cmd
+	if p.lastCmd != nil {
+		cmd = p.lastCmd
+	}
+	p.writeUsageForSubcommand(w, cmd)
 }

 // WriteUsageForSubcommand writes the usage information for a specified
@ -46,7 +63,12 @@ func (p *Parser) WriteUsageForSubcommand(w io.Writer, subcommand ...string) erro
 	if err != nil {
 		return err
 	}
+	p.writeUsageForSubcommand(w, cmd)
+	return nil
+}

+// writeUsageForSubcommand writes usage information for the given subcommand
+func (p *Parser) writeUsageForSubcommand(w io.Writer, cmd *command) {
 	var positionals, longOptions, shortOptions []*spec
 	for _, spec := range cmd.specs {
 		switch {
@ -59,10 +81,22 @@ func (p *Parser) WriteUsageForSubcommand(w io.Writer, subcommand ...string) erro
 		}
 	}

+	if p.version != "" {
+		fmt.Fprintln(w, p.version)
+	}
+
+	// make a list of ancestor commands so that we print with full context
+	var ancestors []string
+	ancestor := cmd
+	for ancestor != nil {
+		ancestors = append(ancestors, ancestor.name)
+		ancestor = ancestor.parent
+	}
+
 	// print the beginning of the usage string
-	fmt.Fprintf(w, "Usage: %s", p.cmd.name)
-	for _, s := range subcommand {
-		fmt.Fprint(w, " "+s)
+	fmt.Fprint(w, "Usage:")
+	for i := len(ancestors) - 1; i >= 0; i-- {
+		fmt.Fprint(w, " "+ancestors[i])
 	}

 	// write the option component of the usage message
@ -123,66 +157,47 @@ func (p *Parser) WriteUsageForSubcommand(w io.Writer, subcommand ...string) erro
 	}

 	fmt.Fprint(w, "\n")
-	return nil
 }

-// print prints a line like this:
-//
-//	--option FOO            A description of the option [default: 123]
-//
-// If the text on the left is longer than a certain threshold, the description is moved to the next line:
-//
-//	--verylongoptionoption VERY_LONG_VARIABLE
-//	                        A description of the option [default: 123]
-//
-// If multiple "extras" are provided then they are put inside a single set of square brackets:
-//
-//	--option FOO            A description of the option [default: 123, env: FOO]
-func print(w io.Writer, item, description string, bracketed ...string) {
-	lhs := "  " + item
+func printTwoCols(w io.Writer, left, help string, defaultVal string, envVal string) {
+	lhs := "  " + left
 	fmt.Fprint(w, lhs)
-	if description != "" {
+	if help != "" {
 		if len(lhs)+2 < colWidth {
 			fmt.Fprint(w, strings.Repeat(" ", colWidth-len(lhs)))
 		} else {
 			fmt.Fprint(w, "\n"+strings.Repeat(" ", colWidth))
 		}
-		fmt.Fprint(w, description)
+		fmt.Fprint(w, help)
 	}

-	var brack string
-	for _, s := range bracketed {
-		if s != "" {
-			if brack != "" {
-				brack += ", "
-			}
-			brack += s
-		}
+	bracketsContent := []string{}
+
+	if defaultVal != "" {
+		bracketsContent = append(bracketsContent,
+			fmt.Sprintf("default: %s", defaultVal),
+		)
 	}

-	if brack != "" {
-		fmt.Fprintf(w, " [%s]", brack)
+	if envVal != "" {
+		bracketsContent = append(bracketsContent,
+			fmt.Sprintf("env: %s", envVal),
+		)
+	}
+
+	if len(bracketsContent) > 0 {
+		fmt.Fprintf(w, " [%s]", strings.Join(bracketsContent, ", "))
 	}
 	fmt.Fprint(w, "\n")
 }

-func withDefault(s string) string {
-	if s == "" {
-		return ""
-	}
-	return "default: " + s
-}
-
-func withEnv(env string) string {
-	if env == "" {
-		return ""
-	}
-	return "env: " + env
-}
-
 // WriteHelp writes the usage string followed by the full help string for each option
 func (p *Parser) WriteHelp(w io.Writer) {
-	p.WriteHelpForSubcommand(w, p.subcommand...)
+	cmd := p.cmd
+	if p.lastCmd != nil {
+		cmd = p.lastCmd
+	}
+	p.writeHelpForSubcommand(w, cmd)
 }

 // WriteHelpForSubcommand writes the usage string followed by the full help
@ -195,55 +210,34 @@ func (p *Parser) WriteHelpForSubcommand(w io.Writer, subcommand ...string) error
 	if err != nil {
 		return err
 	}
+	p.writeHelpForSubcommand(w, cmd)
+	return nil
+}

-	var positionals, longOptions, shortOptions, envOnlyOptions []*spec
-	var hasVersionOption bool
+// writeHelp writes the usage string for the given subcommand
+func (p *Parser) writeHelpForSubcommand(w io.Writer, cmd *command) {
+	var positionals, longOptions, shortOptions []*spec
 	for _, spec := range cmd.specs {
 		switch {
 		case spec.positional:
 			positionals = append(positionals, spec)
 		case spec.long != "":
 			longOptions = append(longOptions, spec)
-			if spec.long == "version" {
-				hasVersionOption = true
-			}
 		case spec.short != "":
 			shortOptions = append(shortOptions, spec)
-		case spec.short == "" && spec.long == "":
-			envOnlyOptions = append(envOnlyOptions, spec)
 		}
 	}

-	// obtain a flattened list of options from all ancestors
-	// also determine if any ancestor has a version option spec
-	var globals []*spec
-	ancestor := cmd.parent
-	for ancestor != nil {
-		for _, spec := range ancestor.specs {
-			if spec.long == "version" {
-				hasVersionOption = true
-				break
-			}
-		}
-		globals = append(globals, ancestor.specs...)
-		ancestor = ancestor.parent
-	}
-
 	if p.description != "" {
 		fmt.Fprintln(w, p.description)
 	}
-
-	if !hasVersionOption && p.version != "" {
-		fmt.Fprintln(w, p.version)
-	}
-
-	p.WriteUsageForSubcommand(w, subcommand...)
+	p.writeUsageForSubcommand(w, cmd)

 	// write the list of positionals
 	if len(positionals) > 0 {
 		fmt.Fprint(w, "\nPositional arguments:\n")
 		for _, spec := range positionals {
-			print(w, spec.placeholder, spec.help, withDefault(spec.defaultString), withEnv(spec.env))
+			printTwoCols(w, spec.placeholder, spec.help, "", "")
 		}
 	}

@ -258,6 +252,14 @@ func (p *Parser) WriteHelpForSubcommand(w io.Writer, subcommand ...string) error
 		}
 	}

+	// obtain a flattened list of options from all ancestors
+	var globals []*spec
+	ancestor := cmd.parent
+	for ancestor != nil {
+		globals = append(globals, ancestor.specs...)
+		ancestor = ancestor.parent
+	}
+
 	// write the list of global options
 	if len(globals) > 0 {
 		fmt.Fprint(w, "\nGlobal options:\n")
@ -273,7 +275,7 @@ func (p *Parser) WriteHelpForSubcommand(w io.Writer, subcommand ...string) error
 		short:       "h",
 		help:        "display this help and exit",
 	})
-	if !hasVersionOption && p.version != "" {
+	if p.version != "" {
 		p.printOption(w, &spec{
 			cardinality: zero,
 			long:        "version",
@ -281,27 +283,13 @@ func (p *Parser) WriteHelpForSubcommand(w io.Writer, subcommand ...string) error
 		})
 	}

-	// write the list of environment only variables
-	if len(envOnlyOptions) > 0 {
-		fmt.Fprint(w, "\nEnvironment variables:\n")
-		for _, spec := range envOnlyOptions {
-			p.printEnvOnlyVar(w, spec)
-		}
-	}
-
 	// write the list of subcommands
 	if len(cmd.subcommands) > 0 {
 		fmt.Fprint(w, "\nCommands:\n")
 		for _, subcmd := range cmd.subcommands {
-			names := append([]string{subcmd.name}, subcmd.aliases...)
-			print(w, strings.Join(names, ", "), subcmd.help)
+			printTwoCols(w, subcmd.name, subcmd.help, "", "")
 		}
 	}
-
-	if p.epilogue != "" {
-		fmt.Fprintln(w, "\n"+p.epilogue)
-	}
-	return nil
 }

 func (p *Parser) printOption(w io.Writer, spec *spec) {
@ -313,30 +301,34 @@ func (p *Parser) printOption(w io.Writer, spec *spec) {
 		ways = append(ways, synopsis(spec, "-"+spec.short))
 	}
 	if len(ways) > 0 {
-		print(w, strings.Join(ways, ", "), spec.help, withDefault(spec.defaultString), withEnv(spec.env))
+		printTwoCols(w, strings.Join(ways, ", "), spec.help, spec.defaultVal, spec.env)
 	}
 }

-func (p *Parser) printEnvOnlyVar(w io.Writer, spec *spec) {
-	ways := make([]string, 0, 2)
-	if spec.required {
-		ways = append(ways, "Required.")
-	} else {
-		ways = append(ways, "Optional.")
+// lookupCommand finds a subcommand based on a sequence of subcommand names. The
+// first string should be a top-level subcommand, the next should be a child
+// subcommand of that subcommand, and so on. If no strings are given then the
+// root command is returned. If no such subcommand exists then an error is
+// returned.
+func (p *Parser) lookupCommand(path ...string) (*command, error) {
+	cmd := p.cmd
+	for _, name := range path {
+		var found *command
+		for _, child := range cmd.subcommands {
+			if child.name == name {
+				found = child
+			}
+		}
+		if found == nil {
+			return nil, fmt.Errorf("%q is not a subcommand of %s", name, cmd.name)
+		}
+		cmd = found
 	}
-
-	if spec.help != "" {
-		ways = append(ways, spec.help)
-	}
-
-	print(w, spec.env, strings.Join(ways, " "), withDefault(spec.defaultString))
+	return cmd, nil
 }

 func synopsis(spec *spec, form string) string {
-	// if the user omits the placeholder tag then we pick one automatically,
-	// but if the user explicitly specifies an empty placeholder then we
-	// leave out the placeholder in the help message
-	if spec.cardinality == zero || spec.placeholder == "" {
+	if spec.cardinality == zero {
 		return form
 	}
 	return form + " " + spec.placeholder
--- a/usage_test.go
+++ b/usage_test.go
@ -50,16 +50,12 @@ Options:
  --optimize OPTIMIZE, -O OPTIMIZE
                         optimization level
  --ids IDS              Ids
-  --values VALUES        Values
+  --values VALUES        Values [default: [3.14 42 256]]
  --workers WORKERS, -w WORKERS
                         number of workers to start [default: 10, env: WORKERS]
  --testenv TESTENV, -a TESTENV [env: TEST_ENV]
  --file FILE, -f FILE   File with mandatory extension [default: scratch.txt]
  --help, -h             display this help and exit
-
-Environment variables:
-  API_KEY                Required. Only via env-var for security reasons
-  TRACE                  Optional. Record low-level trace
 `

 	var args struct {
@ -74,12 +70,11 @@ Environment variables:
 		Values   []float64    `help:"Values"`
 		Workers  int          `arg:"-w,env:WORKERS" help:"number of workers to start" default:"10"`
 		TestEnv  string       `arg:"-a,env:TEST_ENV"`
-		ApiKey   string       `arg:"required,-,--,env:API_KEY" help:"Only via env-var for security reasons"`
-		Trace    bool         `arg:"-,--,env" help:"Record low-level trace"`
 		File     *NameDotName `arg:"-f" help:"File with mandatory extension"`
 	}
 	args.Name = "Foo Bar"
 	args.Value = 42
+	args.Values = []float64{3.14, 42, 256}
 	args.File = &NameDotName{"scratch", "txt"}
 	p, err := NewParser(Config{Program: "example"}, &args)
 	require.NoError(t, err)
@ -237,7 +232,7 @@ func (versioned) Version() string {
 }

 func TestUsageWithVersion(t *testing.T) {
-	expectedUsage := "Usage: example"
+	expectedUsage := "example 3.2.1\nUsage: example"

 	expectedHelp := `
 example 3.2.1
@ -260,233 +255,6 @@ Options:
 	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
 }

-func TestUsageWithUserDefinedVersionFlag(t *testing.T) {
-	expectedUsage := "Usage: example [--version]"
-
-	expectedHelp := `
-Usage: example [--version]
-
-Options:
-  --version              this is a user-defined version flag
-  --help, -h             display this help and exit
-`
-
-	var args struct {
-		ShowVersion bool `arg:"--version" help:"this is a user-defined version flag"`
-	}
-
-	os.Args[0] = "example"
-	p, err := NewParser(Config{}, &args)
-	require.NoError(t, err)
-
-	var help bytes.Buffer
-	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp[1:], help.String())
-
-	var usage bytes.Buffer
-	p.WriteUsage(&usage)
-	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
-}
-
-func TestUsageWithVersionAndUserDefinedVersionFlag(t *testing.T) {
-	expectedUsage := "Usage: example [--version]"
-
-	expectedHelp := `
-Usage: example [--version]
-
-Options:
-  --version              this is a user-defined version flag
-  --help, -h             display this help and exit
-`
-
-	var args struct {
-		versioned
-		ShowVersion bool `arg:"--version" help:"this is a user-defined version flag"`
-	}
-
-	os.Args[0] = "example"
-	p, err := NewParser(Config{}, &args)
-	require.NoError(t, err)
-
-	var help bytes.Buffer
-	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp[1:], help.String())
-
-	var usage bytes.Buffer
-	p.WriteUsage(&usage)
-	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
-}
-
-type subcommand struct {
-	Number int `arg:"-n,--number" help:"compute something on the given number"`
-}
-
-func TestUsageWithVersionAndSubcommand(t *testing.T) {
-	expectedUsage := "Usage: example <command> [<args>]"
-
-	expectedHelp := `
-example 3.2.1
-Usage: example <command> [<args>]
-
-Options:
-  --help, -h             display this help and exit
-  --version              display version and exit
-
-Commands:
-  cmd
-`
-
-	var args struct {
-		versioned
-		Cmd *subcommand `arg:"subcommand"`
-	}
-
-	os.Args[0] = "example"
-	p, err := NewParser(Config{}, &args)
-	require.NoError(t, err)
-
-	var help bytes.Buffer
-	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp[1:], help.String())
-
-	var usage bytes.Buffer
-	p.WriteUsage(&usage)
-	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
-
-	expectedUsage = "Usage: example cmd [--number NUMBER]"
-
-	expectedHelp = `
-example 3.2.1
-Usage: example cmd [--number NUMBER]
-
-Options:
-  --number NUMBER, -n NUMBER
-                         compute something on the given number
-  --help, -h             display this help and exit
-  --version              display version and exit
-`
-	_ = p.Parse([]string{"cmd"})
-
-	help = bytes.Buffer{}
-	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp[1:], help.String())
-
-	usage = bytes.Buffer{}
-	p.WriteUsage(&usage)
-	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
-}
-
-func TestUsageWithUserDefinedVersionFlagAndSubcommand(t *testing.T) {
-	expectedUsage := "Usage: example [--version] <command> [<args>]"
-
-	expectedHelp := `
-Usage: example [--version] <command> [<args>]
-
-Options:
-  --version              this is a user-defined version flag
-  --help, -h             display this help and exit
-
-Commands:
-  cmd
-`
-
-	var args struct {
-		Cmd         *subcommand `arg:"subcommand"`
-		ShowVersion bool        `arg:"--version" help:"this is a user-defined version flag"`
-	}
-
-	os.Args[0] = "example"
-	p, err := NewParser(Config{}, &args)
-	require.NoError(t, err)
-
-	var help bytes.Buffer
-	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp[1:], help.String())
-
-	var usage bytes.Buffer
-	p.WriteUsage(&usage)
-	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
-
-	expectedUsage = "Usage: example cmd [--number NUMBER]"
-
-	expectedHelp = `
-Usage: example cmd [--number NUMBER]
-
-Options:
-  --number NUMBER, -n NUMBER
-                         compute something on the given number
-
-Global options:
-  --version              this is a user-defined version flag
-  --help, -h             display this help and exit
-`
-	_ = p.Parse([]string{"cmd"})
-
-	help = bytes.Buffer{}
-	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp[1:], help.String())
-
-	usage = bytes.Buffer{}
-	p.WriteUsage(&usage)
-	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
-}
-
-func TestUsageWithVersionAndUserDefinedVersionFlagAndSubcommand(t *testing.T) {
-	expectedUsage := "Usage: example [--version] <command> [<args>]"
-
-	expectedHelp := `
-Usage: example [--version] <command> [<args>]
-
-Options:
-  --version              this is a user-defined version flag
-  --help, -h             display this help and exit
-
-Commands:
-  cmd
-`
-
-	var args struct {
-		versioned
-		Cmd         *subcommand `arg:"subcommand"`
-		ShowVersion bool        `arg:"--version" help:"this is a user-defined version flag"`
-	}
-
-	os.Args[0] = "example"
-	p, err := NewParser(Config{}, &args)
-	require.NoError(t, err)
-
-	var help bytes.Buffer
-	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp[1:], help.String())
-
-	var usage bytes.Buffer
-	p.WriteUsage(&usage)
-	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
-
-	expectedUsage = "Usage: example cmd [--number NUMBER]"
-
-	expectedHelp = `
-Usage: example cmd [--number NUMBER]
-
-Options:
-  --number NUMBER, -n NUMBER
-                         compute something on the given number
-
-Global options:
-  --version              this is a user-defined version flag
-  --help, -h             display this help and exit
-`
-	_ = p.Parse([]string{"cmd"})
-
-	help = bytes.Buffer{}
-	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp[1:], help.String())
-
-	usage = bytes.Buffer{}
-	p.WriteUsage(&usage)
-	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
-}
-
 type described struct{}

 // Described returns the description for this program
@ -517,37 +285,6 @@ Options:
 	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
 }

-type epilogued struct{}
-
-// Epilogued returns the epilogue for this program
-func (epilogued) Epilogue() string {
-	return "For more information visit github.com/alexflint/go-arg"
-}
-
-func TestUsageWithEpilogue(t *testing.T) {
-	expectedUsage := "Usage: example"
-
-	expectedHelp := `
-Usage: example
-
-Options:
-  --help, -h             display this help and exit
-
-For more information visit github.com/alexflint/go-arg
-`
-	os.Args[0] = "example"
-	p, err := NewParser(Config{}, &epilogued{})
-	require.NoError(t, err)
-
-	var help bytes.Buffer
-	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp[1:], help.String())
-
-	var usage bytes.Buffer
-	p.WriteUsage(&usage)
-	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
-}
-
 func TestUsageForRequiredPositionals(t *testing.T) {
 	expectedUsage := "Usage: example REQUIRED1 REQUIRED2\n"
 	var args struct {
@ -642,50 +379,6 @@ Options:
 	assert.Equal(t, expectedUsage, usage.String())
 }

-func TestUsageWithSubcommands(t *testing.T) {
-	expectedUsage := "Usage: example child [--values VALUES]"
-
-	expectedHelp := `
-Usage: example child [--values VALUES]
-
-Options:
-  --values VALUES        Values
-
-Global options:
-  --verbose, -v          verbosity level
-  --help, -h             display this help and exit
-`
-
-	var args struct {
-		Verbose bool `arg:"-v" help:"verbosity level"`
-		Child   *struct {
-			Values []float64 `help:"Values"`
-		} `arg:"subcommand:child"`
-	}
-
-	os.Args[0] = "example"
-	p, err := NewParser(Config{}, &args)
-	require.NoError(t, err)
-
-	_ = p.Parse([]string{"child"})
-
-	var help bytes.Buffer
-	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp[1:], help.String())
-
-	var help2 bytes.Buffer
-	p.WriteHelpForSubcommand(&help2, "child")
-	assert.Equal(t, expectedHelp[1:], help2.String())
-
-	var usage bytes.Buffer
-	p.WriteUsage(&usage)
-	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
-
-	var usage2 bytes.Buffer
-	p.WriteUsageForSubcommand(&usage2, "child")
-	assert.Equal(t, expectedUsage, strings.TrimSpace(usage2.String()))
-}
-
 func TestUsageWithNestedSubcommands(t *testing.T) {
 	expectedUsage := "Usage: example child nested [--enable] OUTPUT"

@ -721,8 +414,6 @@ Global options:

 	_ = p.Parse([]string{"child", "nested", "value"})

-	assert.Equal(t, []string{"child", "nested"}, p.SubcommandNames())
-
 	var help bytes.Buffer
 	p.WriteHelp(&help)
 	assert.Equal(t, expectedHelp[1:], help.String())
@ -744,7 +435,7 @@ func TestNonexistentSubcommand(t *testing.T) {
 	var args struct {
 		sub *struct{} `arg:"subcommand"`
 	}
-	p, err := NewParser(Config{Exit: func(int) {}}, &args)
+	p, err := NewParser(Config{}, &args)
 	require.NoError(t, err)

 	var b bytes.Buffer
@ -784,36 +475,7 @@ Options:
 		ShortOnly2 string `arg:"-b,--,required" help:"some help2"`
 	}
 	p, err := NewParser(Config{Program: "example"}, &args)
-	require.NoError(t, err)
-
-	var help bytes.Buffer
-	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp[1:], help.String())
-
-	var usage bytes.Buffer
-	p.WriteUsage(&usage)
-	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
-}
-
-func TestUsageWithEmptyPlaceholder(t *testing.T) {
-	expectedUsage := "Usage: example [-a] [--b] [--c]"
-
-	expectedHelp := `
-Usage: example [-a] [--b] [--c]
-
-Options:
-  -a                     some help for a
-  --b                    some help for b
-  --c, -c                some help for c
-  --help, -h             display this help and exit
-`
-	var args struct {
-		ShortOnly string `arg:"-a,--" placeholder:"" help:"some help for a"`
-		LongOnly  string `arg:"--b" placeholder:"" help:"some help for b"`
-		Both      string `arg:"-c,--c" placeholder:"" help:"some help for c"`
-	}
-	p, err := NewParser(Config{Program: "example"}, &args)
-	require.NoError(t, err)
+	assert.NoError(t, err)

 	var help bytes.Buffer
 	p.WriteHelp(&help)
@ -860,16 +522,10 @@ Usage: example [-s SHORT]
 Options:
  -s SHORT [env: SHORT]
  --help, -h             display this help and exit
-
-Environment variables:
-  ENVONLY                Optional.
-  ENVONLY2               Optional.
-  CUSTOM                 Optional.
 `
 	var args struct {
 		Short            string `arg:"--,-s,env"`
 		EnvOnly          string `arg:"--,env"`
-		EnvOnly2         string `arg:"--,-,env"`
 		EnvOnlyOverriden string `arg:"--,env:CUSTOM"`
 	}

@ -885,39 +541,19 @@ Environment variables:
 	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
 }

-func TestEnvOnlyArgs(t *testing.T) {
-	expectedUsage := "Usage: example [--arg ARG]"
-
-	expectedHelp := `
-Usage: example [--arg ARG]
-
-Options:
-  --arg ARG, -a ARG [env: MY_ARG]
-  --help, -h             display this help and exit
-
-Environment variables:
-  AUTH_KEY               Required.
-`
-	var args struct {
-		ArgParam string `arg:"-a,--arg,env:MY_ARG"`
-		AuthKey  string `arg:"required,--,env:AUTH_KEY"`
-	}
-	p, err := NewParser(Config{Program: "example"}, &args)
-	assert.NoError(t, err)
-
-	var help bytes.Buffer
-	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp[1:], help.String())
-
-	var usage bytes.Buffer
-	p.WriteUsage(&usage)
-	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
-}
-
 func TestFail(t *testing.T) {
-	var stdout bytes.Buffer
+	originalStderr := stderr
+	originalExit := osExit
+	defer func() {
+		stderr = originalStderr
+		osExit = originalExit
+	}()
+
+	var b bytes.Buffer
+	stderr = &b
+
 	var exitCode int
-	exit := func(code int) { exitCode = code }
+	osExit = func(code int) { exitCode = code }

 	expectedStdout := `
 Usage: example [--foo FOO]
@ -927,18 +563,27 @@ error: something went wrong
 	var args struct {
 		Foo int
 	}
-	p, err := NewParser(Config{Program: "example", Exit: exit, Out: &stdout}, &args)
+	p, err := NewParser(Config{Program: "example"}, &args)
 	require.NoError(t, err)
 	p.Fail("something went wrong")

-	assert.Equal(t, expectedStdout[1:], stdout.String())
-	assert.Equal(t, 2, exitCode)
+	assert.Equal(t, expectedStdout[1:], b.String())
+	assert.Equal(t, -1, exitCode)
 }

 func TestFailSubcommand(t *testing.T) {
-	var stdout bytes.Buffer
+	originalStderr := stderr
+	originalExit := osExit
+	defer func() {
+		stderr = originalStderr
+		osExit = originalExit
+	}()
+
+	var b bytes.Buffer
+	stderr = &b
+
 	var exitCode int
-	exit := func(code int) { exitCode = code }
+	osExit = func(code int) { exitCode = code }

 	expectedStdout := `
 Usage: example sub
@ -948,139 +593,12 @@ error: something went wrong
 	var args struct {
 		Sub *struct{} `arg:"subcommand"`
 	}
-	p, err := NewParser(Config{Program: "example", Exit: exit, Out: &stdout}, &args)
+	p, err := NewParser(Config{Program: "example"}, &args)
 	require.NoError(t, err)

 	err = p.FailSubcommand("something went wrong", "sub")
 	require.NoError(t, err)

-	assert.Equal(t, expectedStdout[1:], stdout.String())
-	assert.Equal(t, 2, exitCode)
-}
-
-type lengthOf struct {
-	Length int
-}
-
-func (p *lengthOf) UnmarshalText(b []byte) error {
-	p.Length = len(b)
-	return nil
-}
-
-func TestHelpShowsDefaultValueFromOriginalTag(t *testing.T) {
-	// check that the usage text prints the original string from the default tag, not
-	// the serialization of the parsed value
-
-	expectedHelp := `
-Usage: example [--test TEST]
-
-Options:
-  --test TEST [default: some_default_value]
-  --help, -h             display this help and exit
-`
-
-	var args struct {
-		Test *lengthOf `default:"some_default_value"`
-	}
-	p, err := NewParser(Config{Program: "example"}, &args)
-	require.NoError(t, err)
-
-	var help bytes.Buffer
-	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp[1:], help.String())
-}
-
-func TestHelpShowsSubcommandAliases(t *testing.T) {
-	expectedHelp := `
-Usage: example <command> [<args>]
-
-Options:
-  --help, -h             display this help and exit
-
-Commands:
-  remove, rm, r          remove something from somewhere
-  simple                 do something simple
-  halt, stop             stop now
-`
-
-	var args struct {
-		Remove *struct{} `arg:"subcommand:remove|rm|r" help:"remove something from somewhere"`
-		Simple *struct{} `arg:"subcommand" help:"do something simple"`
-		Stop   *struct{} `arg:"subcommand:halt|stop" help:"stop now"`
-	}
-	p, err := NewParser(Config{Program: "example"}, &args)
-	require.NoError(t, err)
-
-	var help bytes.Buffer
-	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp[1:], help.String())
-}
-
-func TestHelpShowsPositionalWithDefault(t *testing.T) {
-	expectedHelp := `
-Usage: example [FOO]
-
-Positional arguments:
-  FOO                    this is a positional with a default [default: bar]
-
-Options:
-  --help, -h             display this help and exit
-`
-
-	var args struct {
-		Foo string `arg:"positional" default:"bar" help:"this is a positional with a default"`
-	}
-
-	p, err := NewParser(Config{Program: "example"}, &args)
-	require.NoError(t, err)
-
-	var help bytes.Buffer
-	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp[1:], help.String())
-}
-
-func TestHelpShowsPositionalWithEnv(t *testing.T) {
-	expectedHelp := `
-Usage: example [FOO]
-
-Positional arguments:
-  FOO                    this is a positional with an env variable [env: FOO]
-
-Options:
-  --help, -h             display this help and exit
-`
-
-	var args struct {
-		Foo string `arg:"positional,env:FOO" help:"this is a positional with an env variable"`
-	}
-
-	p, err := NewParser(Config{Program: "example"}, &args)
-	require.NoError(t, err)
-
-	var help bytes.Buffer
-	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp[1:], help.String())
-}
-
-func TestHelpShowsPositionalWithDefaultAndEnv(t *testing.T) {
-	expectedHelp := `
-Usage: example [FOO]
-
-Positional arguments:
-  FOO                    this is a positional with a default and an env variable [default: bar, env: FOO]
-
-Options:
-  --help, -h             display this help and exit
-`
-
-	var args struct {
-		Foo string `arg:"positional,env:FOO" default:"bar" help:"this is a positional with a default and an env variable"`
-	}
-
-	p, err := NewParser(Config{Program: "example"}, &args)
-	require.NoError(t, err)
-
-	var help bytes.Buffer
-	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp[1:], help.String())
+	assert.Equal(t, expectedStdout[1:], b.String())
+	assert.Equal(t, -1, exitCode)
 }