Regex Tester & Validator

This regular expression identifies invalid CSS class names by checking for disallowed starting characters or illegal characters within the string. It ensures the class name does not start with a number or symbol (excluding underscores and letters) and flags any subsequent characters that are not Unicode letters, numbers, hyphens, underscores, or that contain whitespace. It is particularly useful for form validation or sanitizing user input in web applications where strict CSS class naming conventions must be enforced.