Ctrl+Shift+N is matching brackets instead of opening a new window. Ctrl+Shift+M is also matching brackets. No custom bindings here.
Both by the looks of it.
HTML, PHP, CSS.
If Ctrl+Shift+N is doing something other than the default, search through your .sublime-keymap files to see which one has rebound it.
Well do we need it? Sublime can do bracket matching too.
Ctrl+Alt+K is what I've set it to for now.