function _bindSequence(combo, keys, callback, action) {

            // start off by adding a sequence level record for this combination
            // and setting the level to 0
            _sequenceLevels[combo] = 0;

            /**
             * callback to increase the sequence level for this sequence and reset
             * all other sequences that were active
             *
             * @param {string} nextAction
             * @returns {Function}
             */
            function _increaseSequence(nextAction) {
                return function() {
                    _nextExpectedAction = nextAction;
                    ++_sequenceLevels[combo];
                    _resetSequenceTimer();
                };
            }

            /**
             * wraps the specified callback inside of another function in order
             * to reset all sequence counters as soon as this sequence is done
             *
             * @param {Event} e
             * @returns void
             */
            function _callbackAndReset(e) {
                _fireCallback(callback, e, combo);

                // we should ignore the next key up if the action is key down
                // or keypress.  this is so if you finish a sequence and
                // release the key the final key will not trigger a keyup
                if (action !== 'keyup') {
                    _ignoreNextKeyup = _characterFromEvent(e);
                }

                // weird race condition if a sequence ends with the key
                // another sequence begins with
                setTimeout(_resetSequences, 10);
            }

            // loop through keys one at a time and bind the appropriate callback
            // function.  for any key leading up to the final one it should
            // increase the sequence. after the final, it should reset all sequences
            //
            // if an action is specified in the original bind call then that will
            // be used throughout.  otherwise we will pass the action that the
            // next key in the sequence should match.  this allows a sequence
            // to mix and match keypress and keydown events depending on which
            // ones are better suited to the key provided
            for (var i = 0; i < keys.length; ++i) {
                var isFinal = i + 1 === keys.length;
                var wrappedCallback = isFinal ? _callbackAndReset : _increaseSequence(action || _getKeyInfo(keys[i + 1]).action);
                _bindSingle(keys[i], wrappedCallback, action, combo, i);
            }
        }
binds a key sequence to an event

@param {string} combo - combo specified in bind call
@param {Array} keys
@param {Function} callback
@param {string=} action
@returns void