Re: Question about font-lock-compile-keywords

[Richard Stallman]

    I don't have any concrete info to help, here. I just thought it seemed a bit
    backwards. More typically, optional args are added in such a way that the
    nil value is more or less compatible with the previous version, without the
    new arg (when feasible).

The change is to handle two cases differently, which previously were
handled the same.  Either way, the new version will be compatible with
the previous version in one case, and incompatible in the other case.