Return any bindings that invoke proc in context context. If proc is omitted or #f, match all bindings in context context. If context is omitted or #f, match bindings regardless of context. If both proc and context are omitted or #f, return all bindings. The return value is a list of binding descriptions. Each binding description is a list: (mouse? contexts modmask keycode-or-butnum press-proc release-or-immediate-proc). mouse? is a boolean, contexts is a list of symbols.