Starting with Leopard, NSTextView added support for rectangular selections and non-contiguous selections. Personally I’ve never used these features. However, they do get in my way.

You make a rectangular selection by holding the option key while you click and drag. For one, this changes the cursor to a crosshair that just looks wrong to me in a text view. Also, it interferes with drag a dropping a copy of some text.

Say I need to duplicate a string. Say I’m implementing initWithCoder: and encodeWithEncoder:. I’ll copy paste a bunch of lines real fast, like:

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-(id)initWithCoder:(NSEncoder*)coder
{
	self = [super init];
	self.value1 = [coder decodeObjectForKey:@"AM_SOMECLASS_VAL1"];
	self.value2 = [coder decodeObjectForKey:@"AM_SOMECLASS_VAL2"];
	self.value3 = [coder decodeObjectForKey:@"AM_SOMECLASS_VAL3"];
	return self;
}
-(void)encodeWithCoder:(NSCoder*)coder
{
	[coder encodeObject: self.value1 forKey:@""];
	[coder encodeObject: self.value2 forKey:@""];
	[coder encodeObject: self.value3 forKey:@""];
}

Instead of typing the keys a second time, I’m going to quickly double click on a key in initWithCoder:, hold down option, and drag the key inside the appropriate line in encodeWithCoder:. That will work just like copy/paste, but I don’t have to switch between mouse and keyboard and it doesn’t erase whatever I have stored on the pasteboard.

Since Apple added rectangular selection, this would screw up a lot as I’d hit the option key too early and it would start a rectangular selection, not a drag-copy.

So I googled for a way to disable this, and boy did I have a hard time. And the solution is the defaults key NSProhibitMultipleTextSelectionByMouse. A google search returns only 3 links, the third one being to an old link to the older AppKit Release Notes.

So finally, here’s the solution. Use this command to disable this in Xcode:

defaults write com.apple.Xcode NSProhibitMultipleTextSelectionByMouse -bool YES

or disable it globally, as I did:

defaults write NSGlobalDomain NSProhibitMultipleTextSelectionByMouse -bool YES

This post is pretty verbose, but I really wanted to discuss this enough to make sure anyone else googling for this problem would find this and save themselves a lot of time.