This doesn't necessarily apply to a specific idea in general, but one capability the HTMLForm class is missing is multi-part forms, i.e., a form where the first part must be submitted, validated, and processed before each successive part. This can technically be done manually, but it'd be smoother if it could be done automatically. The primary usage I'm thinking about with this is something like Extension:TwoFactorAuthentication or Extension:OATHAuth, which attempt two-factor authentication on the login form, but do so by putting an extra field in the login form, even if that user doesn't have two-factor authentication enabled.

I'll probably end up implementing this on my own at some point if nobody else gets to it, but I figured I'd file a bug in case anybody else was thinking of this same feature.

Version: 1.21.x
Severity: enhancement