Validator replace of field value instead of key?

["Bailey, Shane C." <SH...@saic.com>]

 

I can get "{0} is required." to be replaced with a key like
"label.firstName"

but how do I do a replace for a var like email address as in:

{0} is not a valid email?   A key doesn't go in there but the email
submitted

goes in there.

 

In the validation.xml instead of <arg0 key="label.firstName" /> what do I
do?

<arg0 key="{var: ??}" resource="false" />   or something??