See the URL listed for a live example of this. If you have an iFrame that has designMode set to "on" and you call: foo.contentWindow.document.execCommand('fontsize', false, 5) // or any value The function will return true, but will not actually update the text selected/additional text added. Fontsize in general seems to do nothing at all, but still returns true every time execCommand is called. Not sure if this is also a bug, but: if a color is specified in the third parameter of execCommand for say 'backcolor' or 'forecolor', and the color has leading zeroes without a pound sign (ie: 00FFFF), execCommand will again return true but not change the font color. Using the #00FFFF notation will work correctly, but other browsers (firefox and IE) support either. It doesn't seem to make sense to return True if nothing was changed.
With r23922, fontsize already works, but forecolor without '#' still doesn't.
Created attachment 15400 [details] test case The bug URL has a test case, but it references non-existing copies of YUI libraries. This archive contains a complete test case.
Works for me.