From f89698667c0b2138445c719101fe7a4d55764738 Mon Sep 17 00:00:00 2001
From: Alex Flint <alex.flint@gmail.com>
Date: Tue, 5 Jan 2016 13:57:01 -0800
Subject: [PATCH] add custom validation example to README

---
 README.md | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/README.md b/README.md
index 93f2574..4a11914 100644
--- a/README.md
+++ b/README.md
@@ -108,6 +108,18 @@ fmt.Printf("Fetching the following IDs from %s: %q", args.Database, args.IDs)
 Fetching the following IDs from foo: [1 2 3]
 ```
 
+### Custom validation
+```
+var args struct {
+	Foo string
+	Bar string
+}
+p := arg.MustParse(&args)
+if args.Foo == "" && args.Bar == "" {
+	p.Fail("you must provide one of --foo and --bar)
+}
+```
+
 ### Installation
 
 ```shell