What is the correct way to detect whether string inputs contain HTML or not?

Question

When receiving user input on forms I want to detect whether fields like \"username\" or \"address\" does not contain markup that has a special meaning in XML (RSS feeds) or

Answer 1

Regex is still the most efficient way of solving your problem. It doesn't matter what frameworks you plan to use, or are advised to use, the most efficient way would still be a custom regex code. You can test the string with a regex, and remove (or convert) the affected section using htmlcharacter function.
No need to install any other framework, or use some long-winded application.