t(i);
    if (char == _COLON) {
      if (i == start) {
        &#47;&#47; If we see a `:` in the beginning, expect wildcard.
        i++;
        if (host.codeUnitAt(i) != _COLON) {
          error(&#39;invalid start colon.&#39;, i);
        }
        partStart = i;
      }
      if (i == partStart) {
        &#47;&#47; Wildcard. We only allow one.
        if (wildcardSeen) {
          error(&#39;only one wildcard `::` is allowed&#39;, i);
        }
        wildcardSeen = true;
        parts.add(-1);
     