[tempfile]

Depends whether your form submission should expect side effects or not. Most forms submissions have side effects. If the effect is truly idempotent, wouldn't PUT be a better verb? That is also supposed to be idempotent.

[echoangle]

You can’t use PUT as a form action though.

[tempfile]

I always forget this, because it makes no sense. Fair enough!

[diroussel]

GET and QUERY are both idempotent.

[tempfile]

I know, but neither GET nor QUERY may have side effects.

[mring33621]

Hold my beer!