@function _compare-strings($a, $b) {
  $ord: "&:.abcdefghijklmnopqrstuvwxyz0123456789-_";
  @for $i from 1 through max(str-length($a), str-length($b)) {
    $av: str-slice($a, $i, $i);
    $bv: str-slice($b, $i, $i);
    @if $av == "" or $av == null  { @return -1; }
    @if $bv == "" or $bv == null  { @return 1; }
    $ap: str-index($ord, to-lower-case($av));
    $bp: str-index($ord, to-lower-case($bv));
    @if $ap == null and $bp == null { @return 0; }
    @if $ap == null { @return -1; }
    @if $bp == null { @return 1; }
    @if $ap > $bp { @return 1; } @else if $ap < $bp { @return -1 }
  }
  @return 0;
}