mwCustomEditButtons is defined in wikibits.js :

================================================= /var/www/hosts/mediawiki/wiki# grep -inr "mwCustomEditButtons" * skins/common/wikibits.js:320:var mwCustomEditButtons = []; // eg to add in MediaWiki:Common.js [..snip..] =================================================

For the wikipedia, the URL to this file is: http://en.wikipedia.org/skins-1.5/common/wikibits.js

All the best, Nick.

I found the mwCustomEditButtons in wikipedia's "mediawiki:monobook.js" which is designed to add edit tool buttons above edit box. However, in my wiki, a javascript error ocurred when I try to do the same thing. I wonder where the mwCustomEditButtons be difined.

here is code from "mediawiki:monobook.js" in wikipedia:

/* add a redirect button to the edit page toolbar */ if (mwCustomEditButtons) { mwCustomEditButtons[mwCustomEditButtons.length] = { "imageFile": "http://upload.wikimedia.org/wikipedia/en/c/c8/Button_redirect.png", "speedTip": "Redirect", "tagOpen": "#REDIRECT [[", "tagClose": "]]", "sampleText": "Insert text"}; };