docs: def validator(node, value):
          '''
          Colander validator that checks whether a given value is a valid
          is company number.
          For our purposes , we expect a firm number that
          is composed of nine or ten characters like 2028445291.
          Sometimes a company number is formatted with separation marks like 0.400.378.485.
          Therefore, there is also a : Func: ` actoren.validators.kbo_preparer` which transforms such input.
          :raises colander.Invalid: if the value is valid Belgian company number.
          '''
  
          if not re.match(r'^[0-9]{9,10}$', value):
              raise colander.Invalid(
                  node,
                  'Dit is geen correct ondernemingsnummer.'
              )