code: function transExpr(expContent, toFunc) {
    var ret
    expContent = expContent.trim().replace(/\"/g, '\'')
    if (!textParser.isExpr(expContent)) {
      ret = expContent
    }
    else {
      ret = []
      var tokens = textParser.parseText(expContent)
      var isSingle = tokens.length === 1
      tokens.forEach(function (token) {
        if (token.tag) {
          var res = expParser.parseExpression(token.value)
          if (!isSingle) {
            res = '(' + res + ')'
          }
          ret.push(res)
        }
        else {
          ret.push('\'' + token.value + '\'')
        }
      })
      ret = ret.join(' + ')
      if (toFunc !== false) {
        ret = eval('(function () {return ' + ret + '})')
      }
    }
    return ret
  }
docs: transfer expressions
  @param  {String} expContent
  @param  {Boolean} toFunc
  @return {String|Function} ret