Check page action for validation

Hi,

I have some custom validation (inheriting ValidationAttribute) on a CMS property which should trigger if I try to publish a page but which should not trigger if the page is set ready to publish and I then select to withdraw and edit.

Checking the status of the page seems to work in that in this scenario it is CheckedIn but I'm not sure how to differentiate between publishing and withdrawing to edit.

This is probably quite simple but can anyone offer a suggestion on how I might check on the page action to determine whether the validation should trigger or not?

Thanks in advanvce,

Mark