code: function (scanner, tag) {
    if (getClangle(scanner))
      return tag;
  
    if (getSlash(scanner)) {
      if (! getClangle(scanner))
        scanner.fatal("Expected `>` after `/`");
      tag.isSelfClosing = true;
      return tag;
    }
  
    return null;
  }
docs: Try to parse `>` or `/>`, mutating `tag` to be self-closing in the latter case (and failing fatally if `/` isn't followed by `>`). Return tag if successful.