[TYPO3-dev] "POST requests are incompatible with keyword preview." - Why?

[Andreas Kiessling]

Hi all,

we have a frontend form that needs to exchange quite a lot data with 
another page (different page type, json output), so GET is no option 
(eID is also not really an option, we need typolinks in the response).

With POST however, the form does not work, when the page is requested 
with from a "Workspace Preview Link" (so e.g. -> 
https://www.example.com/index.php?&ADMCMD_prev=77d432dd427fb479f186e9caa46c23e1&id=1), 
because the request just dies with the message from the subject.

That line is in tslib_fe since 2006 and i wonder why. The commit message 
was just "Merging all changes from TYPO3_4.0 branch"

I already had a look at the initialization of the preview, but if the 
param is not submitted in the in the url, it falls back to the inputCode 
from a cookie.

Any ideas why POST data is not allowed there? The requests all work 
fine, when using the form from the regular workspace preview.

Regards,
Andreas