code: function isBinding(node, parent) {
    var keys = _retrievers.getBindingIdentifiers.keys[parent.type];
    if (keys) {
      for (var i = 0; i < keys.length; i++) {
        var key = keys[i];
        var val = parent[key];
        if (Array.isArray(val)) {
          if (val.indexOf(node) >= 0) return true;
        } else {
          if (val === node) return true;
        }
      }
    }
  
    return false;
  }
docs: Check if the input `node` is a binding identifier.