[LBXZero]

SPELLS_CHANGED is fired whenever UpdateSpells() is called, which is only used in the Spell Book frame. By my search of all files in FrameXML folder, the only frame that uses SPELLS_CHANGED is the spell book.

For the Spell Book, the SPELLS_CHANGED event causes the 12 buttons in the frame to update images and labels according to the current page. The buttons unregister the event when the spell book is closed. I believe SPELLS_CHANGED was tagged along with various other events and conditions so that the Spell Book will properly update if something occurred that would cause a glitch for the buttons if not updated.

Seeing this, it seems kind of wasteful on performance, but I know the spell book frame was not made for processing efficiency but easier coding. This is not an issue because the spell book should only be open to place spells in the action bar or inserted into macros.