jordanlev/concrete5 — comment on commit 6672c2a36236a38ab818eacaaa1cb76ab219f797
File:  line 0
By Remo:

It starts here:
/concrete/controllers/upgrade.php

and then looks for a php file located in this directory:
/concrete/helpers/concrete5/upgrade

which then pulls the XML schema from this directory:
/concrete/helpers/concrete5/upgrade/db/