code: function(_part){
          if (_part[2]!='in')
              throw 'bad for loop statement: '+_part.join(' ');
          _stack.push(_part[1]);
          // b is array or has [1,2,4],{a:'aaa',b:'bbb'}
          _doParseVars(_part[3]);
          return 'var __HASH__'+_part[1]+' = '+_part[3]+','+
                      _part[1]+','+_part[1]+'_count=0;'+
                 'if (!!__HASH__'+_part[1]+')'+
                     'for(var '+_part[1]+'_key in __HASH__'+_part[1]+'){'+
                          _part[1]+' = __HASH__'+_part[1]+'['+_part[1]+'_key];'+
                          'if (typeof('+_part[1]+')=="function") continue;'+
                          _part[1]+'_count++;';
      }
docs: /*
  解析{for x in b}字符串的前缀
  @param  {Array}  按空格拆分的值,['for','x','in','b']
  @return {String} 解析后的前缀值