What does 'AT!=""' do?

[NickBoots]

Short question, but I can't find documentation on this anywhere I look, feels like it assumes people just know what it does, but I honestly have no clue.

I have seen this in a few examples, like in here.

So, it's always 'AT!=' followed by a string. Most info on AT commands explain what the questionmark does, but none seem to explain the exclamationmark, not even in the Sequens documentation.

[NickBoots]

@robert-hh Super, thank you!

[robert-hh]

@NickBoots AT!="..." is used for Sequans firmware commands. You can get a list with
AT!="help"
The list is long.
AT!="help help"
tells you, how to get only parts of that list and how to use help.