static verifyTagName(tagName) {
    if (!VALID_NAMES_IN_TAG.test(tagName)) {
      throw new Error(
          SafeHtml.ENABLE_ERROR_MESSAGES ? `Invalid tag name <${tagName}>.` :
                                           '');
    }
    if (tagName.toUpperCase() in NOT_ALLOWED_TAG_NAMES) {
      throw new Error(
          SafeHtml.ENABLE_ERROR_MESSAGES ?

              `Tag name <${tagName}> is not allowed for SafeHtml.` :
              '');
    }
  }
Verifies if the tag name is valid and if it doesn't change the context.
E.g. STRONG is fine but SCRIPT throws because it changes context. See
SafeHtml.create for an explanation of allowed tags.
@param {string} tagName
@return {void}
@throws {!Error} If invalid tag name is provided.
@package