Now click the bookmark
It copies the fields from the DOM into some Javascript which goes into the bookmarklet. Clicking it runs the Javascript copying the stuff back again (same named fields, but different page).
It was also straightforward to copy things into URL parameters, like : http://example.org?name=wqe&food=vbn&place=yuiyu
But I can't think of a good use for that either...
It does seem to mess up the browser's grabbing of the favicon and title (maybe just on Chrome), dunno if that can be fixed or not.