##JWToolbarAdaptiveSpaceItem ###Description JWToolbarAdaptiveSpaceItem is an NSToolbarItem subclass that acts as an adaptive spacer for OS X applications with a toolbar and source list or other pane-like structure. Once set up, it will automatically adjust its width to match the width of an attached NSView (most likely the left pane of an NSSplitView) as can be seen in applications like Apple Mail.

###Usage

1. Add JWToolbarAdaptiveSpaceItem .h/.m to your Xcode project
2. Add a blank NSToolbarItem to your window's toolbar
3. With the blank toolbar item selected, select the Identity inspector and change the item's class to JWToolbarAdaptiveSpaceItem
4. Connect the linkedView outlet of the spacer item to the appropriate NSSplitView subview or other relevant NSView
5. That's it! You now have a spacer item that resizes itself through the incredible powers of KVO.

###Recommendations Toolbar customization is best turned off when using JWToolbarAdaptiveSpaceItem because otherwise, the user may place the adaptive toolbar item in locations other than the intended position, causing strange things to occur. Future revisions may address this issue.