_isValidAttribute = function _isValidAttribute(lcTag, lcName, value) {
      /* Make sure attribute cannot clobber */
      if (SANITIZE_DOM && (lcName === 'id' || lcName === 'name') && (value in document || value in formElement)) {
        return false;
      }
      /* Allow valid data-* attributes: At least one character after "-"
          (https://html.spec.whatwg.org/multipage/dom.html#embedding-custom-non-visible-data-with-the-data-*-attributes)
          XML-compatible (https://html.spec.whatwg.org/multipage/infrastructure.html#xml-compatible and http://www.w3.org/TR/xml/#d0e804)
          We don't need to check the value; it's always URI safe. */
      if (ALLOW_DATA_ATTR && !FORBID_ATTR[lcName] && regExpTest(DATA_ATTR, lcName)) ; else if (ALLOW_ARIA_ATTR && regExpTest(ARIA_ATTR, lcName)) ; else if (!ALLOWED_ATTR[lcName] || FORBID_ATTR[lcName]) {
        if (
        // First condition does a very basic check if a) it's basically a valid custom element tagname AND
        // b) if the tagName passes whatever the user has configured for CUSTOM_ELEMENT_HANDLING.tagNameCheck
        // and c) if the attribute name passes whatever the user has configured for CUSTOM_ELEMENT_HANDLING.attributeNameCheck
        _isBasicCustomElement(lcTag) && (CUSTOM_ELEMENT_HANDLING.tagNameCheck instanceof RegExp && regExpTest(CUSTOM_ELEMENT_HANDLING.tagNameCheck, lcTag) || CUSTOM_ELEMENT_HANDLING.tagNameCheck instanceof Function && CUSTOM_ELEMENT_HANDLING.tagNameCheck(lcTag)) && (CUSTOM_ELEMENT_HANDLING.attributeNameCheck instanceof RegExp && regExpTest(CUSTOM_ELEMENT_HANDLING.attributeNameCheck, lcName) || CUSTOM_ELEMENT_HANDLING.attributeNameCheck instanceof Function && CUSTOM_ELEMENT_HANDLING.attributeNameCheck(lcName)) ||
        // Alternative, second condition checks if it's an `is`-attribute, AND
        // the value passes whatever the user has configured for CUSTOM_ELEMENT_HANDLING.tagNameCheck
        lcName === 'is' && CUSTOM_ELEMENT_HANDLING.allowCustomizedBuiltInElements && (CUSTOM_ELEMENT_HANDLING.tagNameCheck instanceof RegExp && regExpTest(CUSTOM_ELEMENT_HANDLING.tagNameCheck, value) || CUSTOM_ELEMENT_HANDLING.tagNameCheck instanceof Function && CUSTOM_ELEMENT_HANDLING.tagNameCheck(value))) ; else {
          return false;
        }
        /* Check value is safe. First, is attr inert? If so, is safe */
      } else if (URI_SAFE_ATTRIBUTES[lcName]) ; else if (regExpTest(IS_ALLOWED_URI$1, stringReplace(value, ATTR_WHITESPACE, ''))) ; else if ((lcName === 'src' || lcName === 'xlink:href' || lcName === 'href') && lcTag !== 'script' && stringIndexOf(value, 'data:') === 0 && DATA_URI_TAGS[lcTag]) ; else if (ALLOW_UNKNOWN_PROTOCOLS && !regExpTest(IS_SCRIPT_OR_DATA, stringReplace(value, ATTR_WHITESPACE, ''))) ; else if (value) {
        return false;
      } else ;
      return true;
    }
_isValidAttribute

@param lcTag Lowercase tag name of containing element.
@param lcName Lowercase attribute name.
@param value Attribute value.
@return Returns true if `value` is valid, otherwise false.