Arguably, this library is too fragile

[timhunt]

Looking at the recent bug fixes, it seems that the way this library works, if anything goes wrong, it causes a fatal error, so you get no CSS at all.

A better strategy might be: Wrap the processing of each rule in a try-catch, and if there is an error, then just leave that rule alone (perhaps insert a CSS comment flagging the problem so it can be debugged - and Moodle coudl scan for those comments, and report them, before minifying the CSS).