Pinned down horizontal scrollbar behavior on Listboxes; also reworded the Area scrollbar behavior sentence a bit to match. Now to actually implement the changes...

area.go

@@ -11,7 +11,7 @@ import (
 )
 
 // Area represents a blank canvas upon which programs may draw anything and receive arbitrary events from the user.
-// An Area has an explicit size, represented in pixels, that may be different from the size shown in its Window; Areas have horizontal and vertical scrollbars that are hidden when not needed.
+// An Area has an explicit size, represented in pixels, that may be different from the size shown in its Window; Areas have both horizontal and vertical scrollbars that are hidden when not needed.
 // The coordinate system of an Area always has an origin of (0,0) which maps to the top-left corner; all image.Points and image.Rectangles sent across Area's channels conform to this.
 // The size of an Area must be at least 1x1 (that is, neither its width nor its height may be zero or negative).
 // 

listbox.go

@@ -9,8 +9,7 @@ import (
 
 // A Listbox is a vertical list of items, of which either at most one or any number of items can be selected at any given time.
 // On creation, no item is selected.
-// Listboxes have vertical scrollbars that are hidden when not needed.
-// [TODO decide horizontal scrollbar behavior; only the Windows HIG explicitly says to do anything about them (in their case, avoid them unless the control has lots of info and is wide enough, such as a multi-column list) (the Mac OS X one says to just make lists wide enough and ellipsize if needed)]
+// Listboxes have both horizontal and vertical scrollbars that are hidden when not needed.
 type Listbox struct {
 	// TODO Select event