code: function(type, value) {
      if (type !== 'attribute' && type !== 'text') {
        throw new TypeError('isBound must provide type "attribute" or "text"');
      }
      var expr = this.binders[type]._expr;
      return Boolean(expr && value && value.match(expr));
    }
docs: Tests whether a value has an expression in it. Something like `/user/{{user.id}}`.