nl_tokens: Binary search tree iterator
pl_tokens: function BinarySearchTreeIterator ( tree , type ) { type = type || 'v' ; if ( type !== 'k' && <mask> !== 'v' && type !== 'e' ) { throw new Error ( 'Incorrect binary search tree iterator type "' + type + '"!' ) ; } this . _type = type ; this . _tree = tree ; this . _last = null ; this . _done = false ; }