Some context first: ABEL (Advanced Boolean Equation Language) is an old hardware description language which has been mainly used in the 80/90s to program CPLDs. Unfortunately I have not found any meaningful information about the history of the language and why the 'flag' keyword has been deprecated (see below).
According to (modern) language reference the 'flag' keyword is obsolete in ABEL HDL. Nonetheless it is used in this listing on wikipedia in the module section with the argument '-r3'?
What was the initial purpose of this keyword and what is the meaning of the string following it?