code: function checkRegex(regex, node, uFlag) {
              let ast;
  
              try {
                  ast = parser.parsePattern(regex, 0, regex.length, uFlag);
              } catch (_) {
  
                  // ignore regex syntax errors
                  return;
              }
  
              regexpp.visitRegExpAST(ast, {
                  onCapturingGroupEnter(group) {
                      if (!group.name) {
                          const locNode = node.type === "Literal" ? node : node.arguments[0];
  
                          context.report({
                              node,
                              messageId: "required",
                              loc: {
                                  start: {
                                      line: locNode.loc.start.line,
                                      column: locNode.loc.start.column + group.start + 1
                                  },
                                  end: {
                                      line: locNode.loc.start.line,
                                      column: locNode.loc.start.column + group.end + 1
                                  }
                              },
                              data: {
                                  group: group.raw
                              }
                          });
                      }
                  }
              });
          }
docs: Function to check regular expression.
  
  @param {string} regex The regular expression to be check.
  @param {ASTNode} node AST node which contains regular expression.
  @param {boolean} uFlag Flag indicates whether unicode mode is enabled or not.
  @returns {void}