I regularly have the use-case for collecting semi-structured data. By this I mean having type annotations for headings that require certain properties to be present.

As this might be rather confusing consider the following example use-cases:

I'm researching which kettle to buy and collect my findings under a heading "research kettles" with one subheading for each purchase candidate. For each of those I want to collect certain properties like wattage or volume as well as unstructured additional comments. Here My idea would be to have the "research kettles" heading prescribe that each subheading "is a kettle" and specify which fields a kettle should have.

Another example would be collecting project ideas and then rating each of those in terms of viability, desirability, and feasibility.

My idea of this feature would be that a heading can define a record type for subheadings which is then realised as a table or something directly below the heading allowing further unstructured data below the heading.