Can't use clean-css compatibility option.

[reedling78]

My minified css files are breaking in IE8. I noticed that you are using clean-css for magnification so I started playing with the clean-css options. I found most of them to work fine through grunt except for "compatibility".

cssmin: {
options: {
compatibility: true
},
minify: {...}
}

Error
TypeError: Cannot call method 'test' of undefined

OS Windows 8

[sindresorhus]

Should be opened on the clean-css issue tracker.

[ademarre]

@reedling78 I had a similar experience with IE8, but ultimately decided it was not a bug.

First, compatibility: true doesn't work. It doesn't take a boolean but rather 'ie7' or 'ie8'.

cssmin: {
  options: {
    compatibility: 'ie7'
  },
  ...
}

Additionally, I was using grunt-pixrem to add a px fallback to rem units for IE8. It turns out the clean-css "advanced optimizations" undo the fallback. It would work to disable the advanced optimizations with the option noAdvanced: true, but it's better to simply run the pixrem task after cssmin. pixrem preserves the minification; it does not restructure the file.

(Ditto for #109)