code: function walkAttributes(html, fn) {
        if (!html) { return }
        var m;
        while (m = RE_HTML_ATTRS.exec(html))
          { fn(m[1].toLowerCase(), m[2] || m[3] || m[4]); }
      }
docs: Minimize risk: only zero or one _space_ between attr & value
  @param   { String }   html - html string we want to parse
  @param   { Function } fn - callback function to apply on any attribute found