What is a line length “soft limit” and how do I interpret this in the PSR-2 convention?

Question

I don\'t understand this part of php\'s PSR-2 convention:

The soft limit on line length MUST be 120 characters; automated style checkers MUST

Answer 1

There is no hard limit in PSR-2.

The MUST (NOT) refers to automated style checkers, not to you as a programmer.

Also note the section that says that no error should be issued when exceeding the soft limit.