Markdown as a semantic runtime, not a text format

Markdown is excellent while it describes things that really are text: heading, paragraph, list, quote, link, image. In that world, conversion to HTML is relatively direct and the problem is mostly presentation.

Publishing systems rarely stay there. Forms, galleries, ads, callouts, comparison tables, legal blocks, embeds, future links, pending assets, and integrations arrive quickly. At that point Markdown is no longer only a text format. It becomes a way for the author to express intent.

When an author writes something like :::newsletter-form, it may look like a component. In a good publishing system it should not mean 'render this React component'. It should mean: at this location in the page, there is an intent to collect newsletter signups.

If the block is intent, the system can connect it to the active integration, selected design, consent rules, preview, and AI help.