I didn't put this in. If you want to do it yourself, you can edit the skins\basicskin.xml file and put the line:
Code:
<Property name="parent" displayName="Parent" type="System.String, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" value="string.Empty" category="Layout" visible="true" defaultCopy="true" />
on line 22 of the file, or anywhere in the FrameSkin/Setup section. It will be in for the next patch anyway. You can do the same in skins\DefaultSkin.xml if that is your preferred frame skin.