OH NO AN IMPORTANT SPACE WAS REMOVED

Probably just one newline is nice

Please attach the PHP doc in the bottom, not in the top

This was actually probably automatically done by my IDE.

This also probably has an indentation problem

(And the lint of course does not says anything)

it seems Phorge indents with two spaces

(And the lint of course does not says anything)

2 spaces

Can I also amend here just an if ($monograms) ?

Sure!

Extension != application, although they often do.

An extension might only have Engine Extensions and stuff.

Also - maybe adding getPHIDclass() or getApplicationClass() to PhabricatorObjectRemarkupRule, and then running the search in reverse will make it easier for application authors?

Also, if we're being pedantic, each argument is supposed to be in a separate line.

this can be just if ($user_firendly_phids), because php.

installed is confusing here

Yes, that wording was intentional. Extensions are allowed to register multi-character monograms, applications (internal) will not. Down the road, I will be using this overridden method to do the check for monogram conflicts.

As for using the Remarkup rule, see what you mean. I went with this because it puts the burden on the application author to register and track their monograms. Also, it opens the door for an extension to register monograms without a remarkup rule, though I couldn't think of a situation where that could happen.