How to handle validation on a combined Radio buttons and Textarea question?

I have a question with a Yes/No response. For example....

Any other comments Yes (value = 1) No (Value = 2)

Below this I have a textarea field. If the user selects Yes, I'd like validation to force them to complete the textarea.
What type of validation should I be selecting here? I couldn't see anything relevant.

I need to do the Validation If, and that needs to be based on the Radio button response, but I'm not clear what type of validation to run? Alphanumeric and only allow a 1 or 2?

Would appreciate your advice. Thank you.
NJ

Are you doing client jquery or server validation?

Neither as of yet, as I note you've advised Client jQuery in your other reply, although I had asked about customising the CSS as the speech bubbles aren't mobile compatible.

Would take your advice on which solution is best. I'd like the validation to be as robust as possible.

Thank you.
NJ

Well server validation is the most solid, since javascript can be bypassed. Client validation is a better user experience and often simpler to implement since you don't have to submit the page. I usually will use both, but on sites that I'm not really worried about hacking and bad values entered maliciously (like admin back ends) then javascript validation is sufficient and you can skip server since it would never be used if the client validation works properly.

I'll use server validation on this particular project then as it's a public front-end submitting personal medical information.

In that case you can use Required validation on the server variable:

<?php echo((isset($_POST["RadioName"]) && $_POST["RadioName"] === "1")?$_POST["TextAreaName"]:"pass"); ?>

Sorry Ray, I'm using the Server Validations Insert wizard here.

My trigger is the pressing of the submit button, validation type is "Required" as you've stated, then I have to select a Server variable...is the code you've provided above what I insert in the "Code" option in the Choose Variable to Validate wizard window?

I've added that and uploaded it to the page but, relating to a post I'd added whilst you were away (when you couldn't get FTP access because of your location), it's not doing the second validation at all.

The secondary validation, healthscreeningform_476, has been applied to this page on a single field - the "Have you consulted your GP for any health related issues in the the past 3 years?" radio button question and the textarea below it in the GP section in Step 2.

Here's the link to the form again. The validation set up on Step 1 works, but any additional validations don't.
http://www.sportsmedicalcertificates.com/health-screening-form.php?tab1=1

Just spotted that the WA Server Validation was inserting the first WA Server Validation title, healthscreeningform_984, in the validation for the second WA Server Validation, healthscreeningform_476.

I've updated that manually and both validation behaviours appear to be working now.

Still a couple of issues though...

I've had to append querystring data to the $WAFV_Redirect so that the correct Bootstrap tab is loaded upon validation failure, as follows:
$WAFV_Redirect = "health-screening-form.php?tab2=1&v=1";

The problem with this is that every time validation takes place it continues to add querystrings to the URL, like this (three validation attempts):
health-screening-form.php?tab2=1&v=1&tab2=1&v=1&tab2=1&v=1

Why isn't it just updating the querystrings, considering that they have the same name?

If you update the <form> tag action to action="health-screening-form.php" that should prevent the repeated parameters.