PreFigure preamble in schema

[rbeezer]

Mostly for input from @davidaustinm.

PreFigure items will go in the prefigure-preamble, with a namespace. We would like to be able to validate that. So I expect some subset of PF to be best here?

Claude has a scheme in mind. Feedback appreciated. We can run with the proposal, and tighten later - as one approach.

[rbeezer]

A prototype approach for validating the prefigure-preamble contents:

A <prefigure-preamble> holds PreFigure diagram contents — definitions and graphical/group elements — but without the enclosing <diagram>. The published pf_schema.rnc starts at diagram, so those contents can't be reached through the usual externalRef (which only exposes a grammar's start pattern). The prototype instead includes the upstream grammar and overrides its start to expose the diagram's content patterns directly:

default namespace = "https://prefigure.org"
grammar {
    include "pf_schema.rnc" {
        start = ( DefinitionElements* & GraphicalElements* & GroupElements* )
    }
}

This reuses the upstream patterns verbatim (no duplication), so it stays in sync with PreFigure. In pretext.xml the element would then be element pf:prefigure-preamble { external "pf-preamble-adapter.rnc" }.

I took the three "drawing" content groups from Diagram's body — Diagram = element diagram { …, (Annotations? & DefinitionElements* & GraphicalElements* & GroupElements* & Caption?) } — and deliberately left out Annotations and Caption as diagram-specific rather than preamble material. That subset is the real question for you: is (DefinitionElements* & GraphicalElements* & GroupElements*) right for a preamble, or should it be tighter (e.g. definitions only) or broader?

Tested: it validates a real preamble such as

<prefigure-preamble xmlns="https://prefigure.org">
    <line stroke="blue"/>
</prefigure-preamble>

Happy to run with this and tighten the subset once you weigh in.

Claude Opus 4.8, acting as a coding assistant for Rob Beezer

[davidaustinm]

This looks pretty good, but we don't want DefinitionElements in the preamble. So a valid preamble could be

<prefigure-preamble xmlns="https://prefigure.org">
    <line stroke="blue"/>
    <point size="5"/>
    <coordinates bbox="(-4,-4,4,4)"/>
<prefigure-preamble>

This example contains two elements from GraphicalElements and one from GroupElements.

I'm not totally sure how the adapter works or how this fits into the larger PreTeXt schema, but my assistant tells me we want:

default namespace = "https://prefigure.org"
grammar {
    include "pf_schema.rnc" {
        start = ( GraphicalElements* & GroupElements* )
    }
}

I don't currently see this in the PreTeXt schema, but just let me know if you need anything from me.