Thanks Darwin! Here's what I'm trying to create a button  for:

-tsaint (October 11, 2008, 07:02 PM)

Opus 8 does not support xml. The copy/paste mechanism for buttons changed with the advent of Opus 9. You'll just need to create  a new button and insert the command into it manually, as others have suggested.

Alternatively, upgrade to Opus 9. :)