how to validate a field on condition?

Hi all,
I have a form with a dropdown menu and a text field.
The text field is disabled until I select a specific value from the dropdown menu.
When I select the right value in the dropdown menu, the text field gets enabled (I used jquery to handle enable/disable) and I need to validate it.
If it's disabled I don't have to validate it.
How can I validate the text field only if it's enabled?
TIA
tony

Are you doing client or server validation for the rest of the form?

Originally Said By: Ray Borduin

  Are you doing client or server validation for the rest of the form?  

I'm doing server side validation.
TIA
tony

In your validation you can use something like: <?php echo($_POST['selectfieldname']=="other")?$_POST['textfieldname']:"n/a"; ?>

That way if the value of the select field is "other" it will validate the text field, but if it isn't it will use "n/a" which would pass validation.

Originally Said By: Ray Borduin

  In your validation you can use something like: <?php echo($_POST['selectfieldname']=="other")?$_POST['textfieldname']:"n/a"; ?>

That way if the value of the select field is "other" it will validate the text field, but if it isn't it will use "n/a" which would pass validation.  

Hi Ray,
thanks for your patience,
where should I put this code?
what kind of validation should I select from the "validation type" list?
TIA
tony

As the validated value. I was thinking you were needing required validation.