it's just been added by me. (it's not xemacs dependent but paredit dependent that i didn't notice due to my shared init.el file).
Just to clarify, paredit has nothing to do with `paren-mode', the latter of which I know nothing about (an XEmacsism?). I don't think any of the patches involved actually mistakenly do anything with paredit, but the commentary is slightly confused/confusing.
fair enough, it was only a wild and quick guess based on a sloppy test against gnu emacs.
it's xemacs only and you can set it to 'sexp-surround to color the entire sexp the caret is in. the patch mimics this in sldb in default mode when marking a stackframe in the source.
sorry for the confusion,