nl_tokens: Track message callback by messageID .
pl_tokens: function MessageTracker ( opts ) { assert . object ( opts ) ; assert . string ( opts . id ) ; assert . object ( opts . parser ) ; this . id = opts . id ; this . _msgid = 0 ; this . _messages = { } ; this . _abandoned = { } ; this . parser = opts . parser ; var self = this ; this . __defineGetter__ ( 'pending' , function ( ) { return <mask> . keys ( self . _messages ) ; } ) ; }