Form text field default & validation

I have been searching for a solution to this dilemma, perhaps I am 
searching using the wrong keywords, I have not found a solution.

I want to validate my form so that the required fields each contain 
data, entered by the submitter.  Accessibility demands that a text 
area field contain default text.  When default text is included for a 
form field it validates automatically, and the submitter does not 
receive a reminder to fill in the required fields.

How can I include default information in the text field AND validate 
that same text field?

Thanks
Donna