code: func (inliner *Inliner) collectElementsAndRules() {
  	for _, stylesheet := range inliner.stylesheets {
  		for _, rule := range stylesheet.Rules {
  			if rule.Kind == css.QualifiedRule {
  				// Let's go!
  				inliner.handleQualifiedRule(rule)
  			} else {
  				// Keep it 'as is'
  				inliner.rawRules = append(inliner.rawRules, rule)
  			}
  		}
  	}
  }
docs: // Collects HTML elements matching parsed stylesheets, and thus collect used style rules