I'm looking for something like http://validator.nu/, I'll be validating html input ( string ) and I want to notify the user if there are any missing end tags, whether a certain element can't have a certain attribute, things of that nature ( HTML 4.01 Strict validation basically ).
Sidenote: I won't be dealing with XML/DTDs, and I don't want to correct the user input like how http://htmlpurifier.org/ does it.