The submit handler for a component's form — the inspector's Configuration tab and the builder's Interface tab are both this form.

It keeps what the form cannot show. A component's attrs and slots are declarations, and the form draws each one's options as a few controls — Required, Default, Doc. A declaration holds more than that, and holds values those controls cannot draw:

• keys with no control at all — values, editor, default_struct, a slot's validate_attrs;
• values a text box draws as nothing — nil, false, true, [] — or as a string — 0, 1.0.

Saved as the controls sent them back, a save rewrote the declaration from what was on screen. A rename of chelekom-button declared attr :type with no default, and the first page that left type unset raised key :type not found.

So once MishkaGervaz.Form.Web.Events.SubmitHandler.Default has parsed the params, every row named like a row the record already declares gets back what the form did not change:

• in an option map (a :key_map sub-field), each key with no control, and each key whose control came back exactly as it was drawn;
• in a list of rows (a :key_list sub-field — a slot's own attributes), each row that came back exactly as it was drawn, whole. Those rows are drawn flat while the record keeps required and doc under opts, and half of one would say both.

Which fields and keys those are is read from the form's own declaration. A control the author did change is theirs, a blank included; a row they renamed or added is new.