The processor can handle html and php files. These files typically end in .php or .html. The processor can also handle html inside php files.
However, all php and html files must be valid. If you are unsure if your html is valid, run it through the
W3C validator. If you can't execute your php script, it may not be processed correctly. If you have a php program divided among many scripts(using includes or requires), each one can be processed individually with no problem.