Less language is an extension of css and less4j compiles it into regular css. Less adds several dynamic features into css: variables, expressions, nested rules, and so on. Less was designed to be compatible with css and any correct css file is also correct less file.
I'm using 1.17.1 and getting this error
ERROR 10642:5 no viable alternative at input '>' in ruleset (which started at 10624:1)
on the line marked below:
This does not cause a problem with lessc. Changing the problematic line to this resolves the error:
.xFillSpace(@width: ~"calc(100% + @{formResponsiveGridLayoutHalfGutterWidth})");
[edited after initial post with more info]