code: function(sel, context) {
    // split up groups
    if (~sel.indexOf(',')) {
      var sel = sel.split(/,\s*(?![^\[]*["'])/)
        , res = []
        , s = 0
        , sl = sel.length;
  
      for (; s < sl; s++) {
        var cur = select(sel[s], context)
          , c = 0
          , cl = cur.length;
        for (; c < cl; c++) {
          var item = cur[c], rl = res.length;
          while (rl-- && res[rl] !== item);
          if (rl === -1) res.push(item);
        }
      }
      return res;
    }
  
    var i = 0
      , res = []
      , test = compile(sel)
      , scope = context.getElementsByTagName(test.qname)
      , el;
  
    while (el = scope[i++]) {
      if (test(el)) res.push(el);
    }
    return res;
  }
docs: Selection