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

filter_input + FILTER_SANITIZE_STRING (there are lots of flag you can chose from)

:- http://www.php.net/manual/en/filter.filters.sanitize.php