[pmwiki-users] find out if pagetextvariable is set

[noskule]

hi list
is it possible to find out via conditional markup if a pagetext variable
ist set even if is has no value?

for the ptv {*$:ptv}
this should result in true:
(:ptv: :)

this should result in true to:
(:ptv: 123:)

if there is no ptv it I should get false.

thanks for any hints
nos