Question

Does anyone have this Regular Expression?

 public static class HtmlAttributeValidator{

     const bool REGEX_OPTIONS = RegexOptions.WhatGoesHere;

     const string VALID_ATTRIBUTE_REGEX = @"What goes here?";

     public static bool IsValidHtmlAttributeValue(string attributeValue){
           return Regex.Match(attributeValue ?? string.Empty, 
                              VALID_ATTRIBUTE_REGEX, 
                              REGEX_OPTIONS);
     }

 }

Answer 1

You will not find such a regular expression, because many attribute values can take any valid textual value, hence the values are not regular and can’t be matched by a regular expression.

See this list of HTML attributes and the values they can take. In particular note the ones that take CDATA values:

CDATA is a sequence of characters from the document character set and may include character entities.