When is a php include file parsed?

Question

When is a PHP include file parsed? At startup, or during execution?

My web forms call a single php script. Depending on the arguements passed in the URL, a swit

Answer 1

Files are included if and when the include statement is reached at runtime. To very succinctly summarise what that means, the following file is never going to be included:

if (false) {
    include 'foo.php';
}