Markup

The tree a producer emits.

The vocabulary is one thing but reaches a page two ways — as DOM built by the custom element, and as HTML written by a server. Describing the tree instead of building either one is what lets both say the same thing: the tags, the attributes and the nesting are decided once, in TranscriptMarkup, and a producer only knows how to walk this.

There are two leaves, and the difference between them is the point. Markup.Text is what a person or an agent wrote, which every producer escapes. Markup.Html is markup this module produced, and it can hold nothing but a Prose — a type no caller outside the transcript package can construct from transcript text. So a producer is never left deciding which of the two a value is.