canAcceptMessages ?

Someone can explain what's the purpose of "canAcceptMessages" for controllist and button class in xbmcgui  ?
May be a sample ?
with it, Can we add, an action when a key is pressed for an existing control ?

I would to show a dialog context menu when 'c' or 'm' is pressed but for existing control list in skin .....
but only oninfo, onup,onback,onleft,onright,ondown and onclick are available in XML skin code.....

thanks