Format of compilation-error-regexp-alist-alist

[Lennart Borgman]

I do not understand the format of `compilation-error-regexp-alist-alist. 
I can not find in the documentation how the first element in the entries 
are used. Where is absoft, ada, aix etc used? If I want to add a new 
entry to the alist for support of a new command what should this new 
command output to match the names (absoft, ada etc)?

Am I missing something in the documentation?