code: function(attrName) {
      return function(err, validationErrMsg) {
        ranCount++
        if (returned) return
  
        // If error, return, and set `returned` to true.
        if (err) {
          returned = true
          return done(err)
        }
  
        // Add the validation error to the object `validationErrors`
        if (validationErrMsg) {
          self._merge(validationErrors, validationErrMsg, (prefix || '') + '.' + attrName)
          isValid = false
        }
  
        if (ranCount === attrNames.length) _runAfter()
      }
    }
docs: ====== (step II) ====== Run validators for all attributes, and collect validation errors