string validation/ form validation

[OriginalBrownster]

Hi there:

I just had a quick thought of something that might be useful to me when
creating my web app and I wanted some help on the idea; since this
group has been helpful in the past.

in my app I have a few html forms that require the user to enter in
data, in string form

is it possible to validate if the string is in a valid form..such as
check if its a list

An example

ask the user to enter in a list seperated by commas

so i want something like "apple,banana,grapes"

is there a way to validate that it was entered that way?

Any help would be appreciated