Thread:User talk:Superm401/VisualEditor Parsoid.php revert/reply

It's in the root of the Parsoid repository. See https://git.wikimedia.org/blob/mediawiki%2Fextensions%2FParsoid.git/HEAD/Parsoid.php. Specifically, that is a symbolic link. If your system does not support symbolic links, you can instead use php/Parsoid.php (that's where the symbolic link points to).