What clean means, stated precisely
No framework pulled in as a dependency of a dependency, no emoji-detection scripts, no block library, no theme payload. Headings that are actually headings, in the order the argument runs. Sections that are actually sections. Landmarks present. Link text that says where the link goes. Interactive states expressed as real style rules, so a keyboard user and a mouse user get the same page.
A document written the way a careful developer would write it by hand, produced automatically.
The outline is the argument
A heading structure is the compressed argument of a page, which is why a broken one costs more than it appears to. Levels run in order without skipping. A heading earns the tag by heading something, rather than by somebody wanting larger text. The visual hierarchy and the document outline agree, since a page where they disagree is telling a person one thing and a machine another.
"Read aloud by a screen reader, the outline should make sense on its own."
That test is also the test for whether a retrieval system can find where an argument begins.
Passage extraction gets easier
Systems that sit between people and the open web answer questions directly, cite sources and summarize pages. They work by pulling candidate passages out of documents and deciding which to trust. A passage inside a cleanly bounded section with a descriptive heading is straightforward to extract. The same passage buried inside nested wrapper elements is not. On a page the protocol renders, the argument is very nearly the only thing in the document, which makes it the most legible thing a parser encounters.
Structured data generated from the finished page
Machine-readable facts are produced from the published piece rather than typed into a form. Article markup describes the article as it stands. Questions come from the questions the page addresses. Procedure steps mirror the steps actually listed. Contact details come from one settings source that feeds both the visible page and the markup, so the two can never disagree.
That removes the most common structured data failure, which is markup describing a version of a page that was edited months ago. A machine told one thing while a reader is told another is worse than no markup at all.
Accessibility arrives with the document
Proper heading order, descriptive link text, alternative descriptions on images, visible and logical focus, present landmarks and adequate contrast are accessibility requirements, and they are also exactly the structures that make a document parseable. Because they are properties of what the protocol emits, they arrive by construction rather than through a remediation project. Nobody schedules an accessibility phase to undo the way a site was built.
Remediating a site somebody else built is a different exercise entirely, covered in search engine compliance under organic search marketing. The concern here is what a document contains when it is produced correctly from the start.
What is deliberately not editable
Icons and structural decisions are code. Navigation link lists are menus. Contact details come from one source feeding both the page and its structured data. An editable region exists only where a human will plausibly want to change something, because every region is a decision somebody has to make later without a designer in the room.
Where markup work connects
What the document leaves out is covered in zero CSS bloat, the contract describing its regions is covered in composer blueprints, and the media it references is covered in aggregated assets.
How the engagement runs
Markup work happens through screen shared sessions, and the honest way to evaluate it is to view the source of a page the protocol produced and compare it against your current site. If your pages are structurally sound to a person and unreadable to a parser, the document is the place to look.