code: function tag(name, tmpl, css, attrs, fn) {
        if (isFunction$1(attrs)) {
          fn = attrs;
  
          if (/^[\w-]+\s?=/.test(css)) {
            attrs = css;
            css = '';
          } else
            { attrs = ''; }
        }
  
        if (css) {
          if (isFunction$1(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