The platform's load process diagram does not render on the published site

[jwrosewell]

The problem

The load process diagram on the preference platform's documentation is a
mermaid sequence diagram, and it does not render on the published site. The
site shows it as a code listing.

What was checked

• docs/Doxyfile has PLANTUML_JAR_PATH empty, at line 2638, and neither
  docs/Doxyfile nor docs/header.html mentions mermaid.
• The generator is the customised Doxygen 1.8.15, which has no mermaid
  support of its own.
• The diagram is on src/identifiers/pmp/index.md at line 77 on the
  documentation branch
  (#238). It uses the
  bare mermaid fence so that GitHub renders it in the pull request, and the
  page carries the same sequence as numbered steps underneath, so nothing is
  lost on the site today.

Why it needs a decision rather than a quick change

Making it render means loading mermaid from docs/header.html. That header
is used by the Doxyfile of other repositories as well as this one, for
example pipeline-dotnet/docs/Doxyfile and rust/docs/Doxyfile, so the
change reaches every repository's generated documentation. It also adds a
script the documentation pages would load from a CDN. Both are worth
deciding on purpose.

Related

• The documentation work package, #237
• The create last programme, which is tracked internally