ADR-041 makes section the base that compositions place. The page-section runes (hero, cta, feature, pricing, reveal, tabs, accordion, steps) are expected to become compositions over it in time. Whatever section does with a leading paragraph or heading then becomes the header grammar of that whole family.

Today the family has two grammars, and they disagree:

Content	Native page-section runes (`pageSectionProperties`, `packages/runes/src/tags/common.ts`)	`section` (`packages/runes/src/tags/section.ts`)
Paragraphs, no heading	the first paragraph is the blurb	the first paragraph is the eyebrow
Paragraph, then heading	eyebrow, then headline	eyebrow, then headline
Two headings	the first heading is the eyebrow	the second heading is body
Heading, then prose, then a paragraph	the first paragraph after the heading, anywhere, is the blurb	only a paragraph directly after the heading is the blurb

Composition makes section's grammar read content that was never written as a header. A host runs its content model over the expanded template, so an author's paragraph arriving through a slot is matched by position like anything else:

SPEC-169 D4's steps example places each step with {% section %}{% slot /%}{% /section %}. A step's text is a paragraph with no heading before it, so section renders it as an eyebrow: small, uppercase, in the primary colour.
A composed testimonial (SPEC-161 D1) that places its quote and attribution slots in a section gets the quote as the eyebrow and the attribution as the blurb.
The composed character, realm and faction escape only because their template places {% metablock %} between the heading and the description slot. Without it, the description's first paragraph would become a blurb. Nothing would report it.

A standalone section has the same problem, and WORK-652 makes it more common. With a media split, section becomes the general "region with media" primitive. An image beside two paragraphs then renders the first paragraph as an eyebrow.

Options Considered

(a) Accept positional matching

Record each case as an explained difference. Rejected: every case above is a misreading the author did not ask for and cannot see coming.

(b) Header roles come only from slots named for them

Inside a placed host, a header role is filled only by text the template wrote itself, or by a slot whose name is the role's. Other slot content goes to the body. The slot markers SPEC-145 D10a puts on the AST make this implementable. Rejected, for four reasons:

The same markup means different things on a page and in a template. A snippet pasted from a template body into a page changes meaning. SPEC-170 D2 rejected separate template and page parsers for exactly this reason.
It depends on invisible markers. Neither inspect nor reference would show why a paragraph is or is not a blurb.
It couples input vocabulary to host roles. A composition's field names are what its authors write and read in reference. realm would have to rename description to blurb to get the role, renaming its input for a styling reason.
It does nothing for a standalone section.

Its strength, that a composition is correct without its author remembering anything, is kept by the diagnostic in decision 3.

(c) An explicit attribute on `section`

Chosen, together with an anchored grammar and a diagnostic.

Decision

The grammar is anchored to the headline. Eyebrow and blurb exist only relative to a headline. With no heading there is no header: all content is body. An eyebrow is a paragraph directly before the headline, and a blurb is a paragraph directly after it.
section takes header:
- auto (the default) reads eyebrow, headline and blurb as in decision 1;
- headline lifts only the headline, so the paragraph after it stays body;
- none reads no header at all: the region is all body.
The attribute applies wherever section is used, standalone or placed by a composition. A composition sets it like any other attribute, for example {% section header="headline" %}.
A slot that lands in a header role it is not named for is reported. At transform time, when content carrying a slot marker fills a header role and the slot's name is not that role's, the build warns, naming the composed rune, the slot, the role and both remedies. For example: "slot description of character is read as section's blurb; name the field blurb, or set header="headline" on the section." The warning changes nothing that renders.
The page-section runes keep their native grammar until each one becomes a composition. A composed page-section rune parses its author's content with its own content model and places the result. It does not inherit pageSectionProperties' rules through section.

Rationale

The anchoring alone fixes every misreading found: the steps and testimonial cases and the standalone region with media. None of them has a heading.
An attribute is visible and portable. It shows in the source, in inspect and in reference, and means the same thing on a page and in a template.
The diagnostic is precise. The slot markers are already on the AST, so the check sees exactly which slot filled which role, with no static guessing about what a slot may contain.
Deciding on section now is cheaper than later. Every composition placed on it after this inherits the grammar, and changing it then would move every one of them.

Consequences

section's output changes for content with no heading: a leading paragraph that rendered as an eyebrow is now body. The site's existing section examples all have a heading, but the changeset names the change for third-party content.
SPEC-169 D4's steps example renders its steps as body.
header is a new attribute on section. reference documents it, and the editor offers it.

Open questions

A heading used as an eyebrow. hero, cta and feature read two headings as an eyebrow heading and a headline. section's eyebrow is a paragraph only, so a composed hero that places a heading eyebrow would get the wrong headline. This is the one case where (b)'s binding by name is cleaner. It is decided with SPEC-160 D7, when hero and cta become compositions. The options are an eyebrow field that also takes a heading followed by another heading, or a composed hero that turns its heading eyebrow into a paragraph.

References

ADR-041: section is the composition base.
SPEC-160: D9 records this decision; D7 carries the open question.
SPEC-145: D10a (slot markers); the host's positional grammar reads the template's arrangement.
SPEC-169: D4's steps example.
SPEC-170: D2, one meaning for a snippet wherever it is pasted.
WORK-659: the implementation.

Relationships

Context