对正则表达式练习器的改进，原贴ID901680

覆盖原execIt函数
修改后的execIt函数允许对多个正则表达式进行匹配(每个正则表达式一行)，并对每一个匹配成分显示出是第几个正则表达式匹配的。
这可视为语法分析的雏形，只要对匹配产生相应的动作。

function execIt(form) {
  var mode
  if(form.chkmode.checked) mode = "gi"
  else mode = "g"
  var regexpArray = form.regexp.value.split("\r\n")  //获取正则表达式到数组

  if(nextpoint == 0) form.reglist.value = ""
  var key = true
  if(form.scankmode.checked) key = false
  else nextpoint = 0
  do {
    var offs = 9999999999
    var pos = -1
    var input = form.main.value.substr(nextpoint)
    //对每个正则表达式进行匹配
    for(var i=0;i<regexpArray.length;i++) {
      re.compile(regexpArray[i],mode)
      var matchArray = re.exec(input)
      if(matchArray) {
        if(offs > matchArray.index) {
          offs = matchArray.index
          pos = i  //保存距离起始位子最近的匹配
        }
      }
    }
    if(pos>=0) {
      re.compile(regexpArray[pos],mode)
      var matchArray = re.exec(input)
      for(var i=1;i<matchArray.length;i++)
        matchArray[i] = "$"+i+":"+matchArray[i]
      form.reglist.value = "["+(pos+1)+"]"+(nextpoint+matchArray.index)+" => " + matchArray[0] +"\n"+form.reglist.value
      form.matchlist.value = "$0:"+matchArray.join("\n")
      nextpoint = nextpoint + matchArray.index + matchArray[0].length
    }else {
      if(!key)
        form.reglist.value = "没有找到\n" + form.reglist.value
      form.matchlist.value = " "
      nextpoint = 0
      key = false
    }
  }while(key)
}