code: function tag$1(name, tmpl, css, attrs, fn) {
    if (isFunction(attrs)) {
      fn = attrs;
  
      if (/^[\w\-]+\s?=/.test(css)) {
        attrs = css;
        css = '';
      } else
        { attrs = ''; }
    }
  
    if (css) {
      if (isFunction(css))
        { fn = css; }
      else
        { styleManager.add(css); }
    }
  
    name = name.toLowerCase();
    __TAG_IMPL[name] = { name: name, tmpl: tmpl, attrs: attrs, fn: fn };
  
    return name
  }
docs: Create a new riot tag implementation
  @param   { String }   name - name/id of the new riot tag
  @param   { String }   tmpl - tag template
  @param   { String }   css - custom tag css
  @param   { String }   attrs - root tag attributes
  @param   { Function } fn - user function
  @returns { String } name/id of the tag just created