Source code files have version numbers - Kosudo/nextSIS GitHub Wiki

Each source code file has a version number, but this does not have to be the latest version number of the overall product. For example, nextSIS may reach version 1.1.2, but use a version 1.0.9 version of the index.php file.

For php files that will display full pages I'm coding this version number in as a variable, e.g.

$page_version = "0.0.1"; // this is used in the page footer for diagnostic purposes

The purpose is to use a standard footer include file (inc.footer.php) to display the version number of the page for diagnostic purposes.

For minor include files that only have code snippets I'm just using the version number as a comment:

* page_version = 0.0.1