code: function visit(dom, callback) {
              if(Array.isArray(dom) && callback && typeof callback.visitNode === 'function') {
                  for(var i = 0; i < dom.length; i++) {
                      var ret = visitNode(callback, dom[i], null);
                      endVisitNode(callback, dom[i]);
                      if(ret === this.BREAK) {
                          return;
                      }
                  }    
              }
          }
docs: Visit the given AST top-down node -> attributes -> value -> end visit
  @param {Object} dom	The AST to visit
  @param {Function} callback The visitor callback