validation - Flex 4 create validator that allows only letters and dashes? -

how can create validator allows letters dashes input?

thanks in advance

edit

this have far..

if write test passes , if write 123 fails if write test123 passes don't want

edit

the validator works wanted. :)

override protected function dovalidation(value:object):array         {             results = [];              var regex:regexp = /^[a-za-z _-]*[a-za-z][a-za-z _-]*$/;              if(regex.test(value string)) {                 trace("passed")                 return results;              } else {                 var err:validationresult = new validationresult(true,"","","only letters allowed");                 results.push(err);                 trace("error")             }          return results;     } 

ok correct re ^[a-za-z _-]*[a-za-z][a-za-z _-]*$