docs: function (bind) {
                  if (bind.to == null) {
                      // bind.to is mandatory
                      this.$logError(this.MISSING_TO_BINDING);
                      return false;
                  }
  
                  var bindedValue = bind.inside[bind.to];
                  if (bindedValue == null || ariaUtilsType.isBoolean(bindedValue)) {
                      // If it is bound to something that doesn't exist or a boolean, it is valid
                      return true;
                  }
  
                  this.$logError(this.INVALID_TO_BINDING);
                  return false;
              }