The sentence in question:
While it is obvious what it means, I am wondering how precisely it is constructed grammatically.
The textbook way of expressing "must not do" using いけない is:
[て-Form] は いけない
So going by that I would construct it as follows:
出る → 出ちゃう → 出ちゃって → 出ちゃってはいけません
So I assume 「出ちゃいけません」 is simply a shortened form of this grammar.
Is that correct?
If yes, is this common?
If no, how is 「出ちゃいけません」 made up grammatically?