Based on the source[1] it currently trims:

• '; ' => ';'
• ': ' => ':'
• ' {' => '{'
• '{ ' => '{'
• ', ' => ','
• '} ' => '}'
• ';}' => '}'

That still leaves room for improvement of 3 cases (found out through bug 35492).

• Space before }

> return CSSMin::minify("foo { prop: foo }");
foo{prop:foo }

• Space before :

> return CSSMin::minify("foo { prop : foo; }");
foo{prop :foo}

• Space before ;

> return CSSMin::minify("foo { prop: foo ; }");
foo{prop:foo }

• Space before ,

> return CSSMin::minify("foo { prop: foo , bar ; }");
foo{prop:foo ,bar }

Especially the latter two (space before comma or semi-colon) are a fairly common programming style by the "space-extremists".

foo {
    prop:
      voo( .. ) ,
      voo( .. ) ;
    prop: foo ;
}

I'm not going to be bold on this one because I haven't checked whether there are any side-effects to these 4 changes, but they seem easy gains :)

[1] https://svn.wikimedia.org/viewvc/mediawiki/trunk/phase3/includes/libs/CSSMin.php?revision=110557&view=markup#l210

Version: 1.17.x
Severity: enhancement