The dialog logic is a little convoluted right now, primarily due to the introduction of logic to manage the sections separately from the fields.

Instead:

Dialog spec will get a new attribute, sections.
for a dialog, the fields and sections attributes are mutually exclusive. If someone defines a fields attribute, we will assume a sections collection of length one. If someone defines both a sections and fields collection, the builder will error out.

All the logic currently embedded in the dialog and add_dialog will be extracted into the section object.