On Sat, Aug 22, 2015 at 6:04 AM, Stefan Monnier 
<monnier@iro.umontreal.ca> wrote:
> The question was not whether the regexp works, but what does the CSS
> language want us to do.  I.e. is "url(foo)bar)" equivalent to
> "url('foo)bar')" or to "url('foo')bar)"?

Ah, good that you asked, because the CSS spec states the following:

  Some characters appearing in an unquoted URI, such as parentheses,
  white space characters, single quotes (') and double quotes ("),
  must be escaped with a backslash so that the resulting URI value is
  a URI token: '\(', '\)'.

So in "url(foo)bar)", the URI ends at the first ")", while in
"url(foo\)bar)", it ends at the last ")".

The following regexp seems to handle this:

"url\\((\\)[[:space:]]*\\(?:\\\\.\\|[^()[:space:]\n'\"]\\)+[[:space:]]*\\()\\)"

-- Simen