I'm working on a project that requires state to be passed via form fields (i.e. a multi-step wizard.) This means that I end up needing to pass hidden form fields from page to page. This normally requires a funky series of if/elses to determine which values to include on each form. Also, as things change from one form to another, you'd need to update each page in the process to include the hidden form field required, otherwise the value gets lost.
Anyway, I started thinking it would be nice if I didn't have to write any if/else statements and just have the necessary fields required automatically passed. Well, if you're thinking "Why not just loop over the form scope?" Well, that's only part of the solution. You really need to exclude fields that are already on the page.
Fortunately, several years ago I had written some code that was part of a much bigger project, that could parse a string and find form fields and extra information about about the fields. Harvesting the code I had already written, I was able to whip out a tag that would parse the content between the start/end tags, look for any form fields in the content and exclude those fields from being copied as hidden form fields.