code: function INTEGER_VALIDATOR(v) {
    v = (v || '').toString()
  
    if (v.match(/^[-+]?\d+$/)) {
      return {value: parseInt(v, 10)}
    }
  
    return {
      value: null,
      reason: function reason(k, v, result) {
        return 'ERROR: property value `' + v + '` is not supported for `' + util.camelCaseToHyphened(k) + '` (only integer is supported)'
      }
    }
  }
docs: only integer value is valid
  
  @param {string} v
  @return {function} a function to return
  - value: number|null
  - reason(k, v, result)