[Hwona]

Umm? Are you talking about something like DOMAIN.SCRIPTPATH?
I'm taking these from the inc/config.php file. I've never used these before, but if you add include("../inc/config.php"); to each page, you should be able to fetch DOMAIN and SCIPTPATH.
If that doesn't work, you could still try your actual domain... though that's not ideal.

Edit: Also found this $mysidia->path->getAbsolute()
It should work if you've added the $mysidia = Registry::get("mysidia"); to the page.
Try:
$TableForm = new Form("multiform", "{$mysidia->path->getAbsolute()}page/action", "post");