The grammar of “Sorry”

Grammar rules!

Some tricky examples of grammar trip-upsHilfield cross are:
Bored with (not bored of)
Different from (not different than)
Jump off a log (not jump off of ….)

But when it comes to the grammar of saying sorry, what rules apply?

Sorry is hard enough to say, or write, without letting it get buried in undergrowth.

Therefore, sorry has to stand alone. No prepositions. No prefixes or suffixes.

No:
Sorry, but …
or
Sorry – you must understand …
or
Sorry, OK, so it may have been my fault …
or
Sorry – yes, all right, you win, again …
Just sorry.
On its own.