Proposed immutable.css functionality/API.

app.css

.u-i-will-be-opened-twice {
  color: yellow;
}

.u-actually-immutable-selector {
  content: 'I am not being reopened';
}

.awesome {
  font-variant: small-caps; /* Raises linting error (opened vendor.css selector) */
}

.u-i-will-be-opened-twice {
  background-color: red; /* Raises linting error (re-opened a util selector) */
}

linting.js

immutableCss.lint('vendor.css', 'app.css', { immutablePrefixes: ['.u-'] })

vendor.css

.awesome {
  color: green;
}

Okay, I think this makes more sense now...

You're too fast, i'll move convo over to your repo