@function _normalize-include($section) {
// Check if $section is in the $include list.
  @if index($_normalize-include, $section) {
    @return true;
  }
// If $include is set to (all), make sure $section is not in $exclude.
  @else if not index($_normalize-exclude, $section) and index($_normalize-include, all) {
    @return true;
  }
  @return false;
}