Index.html OR index.php

Hi there
Right this may be a stupid question but i’ll ask anyway…
I have a main fla file that loads in various .swf files when a menu button is pressed. THe actual main fla file doesn’t actually call any php scripts. All the php scripts are called within the swf files that are loaded in by the main fla. So, my question is: does the index file need to be .htnl or .php? I have it as .html as I figure no actual php scripts are being called directly from the main fla. Is this wrong??