Yes, it is important to maintain a valid XML file at all times, or your skin will not work. By valid, I mean, for every opening tag there must be a corresponding closing tag.

So if you remove a "<Element ..>" tag, you must also remove the corresponding "</Element>" tag, or the XML file will no longer be valid. Likewise, if you remove a "</Element>" tag, you must also remove the corresponding "<Element>" tag.

(Note that in the case of an "<Element ... />" tag, there is no closing tag, because the "/" takes the place of the closing tag.)

Thanks!
 

All this stuff REALLY helped, thanks. I was just wondering if you knew of any plugins or anything that could help with testing UI parts that aren't always on-screen. Like the quest actions button and such? I was just wondering, if there is anything of the kind please let me know, thanks. :)

I don't know anything which does that, sorry.