Bootstrap 5 and Bootswatch as a model on the runtime's HTML model: documents with themes,
layout, and components for content, navigation, overlays and forms, described by what they
mean and expanded to HTML by BootstrapStructure. The Nasdanika Zephyr Book of the HTML and
Bootstrap models, "HTML and Bootstrap Models", is built from src/docs/asciidoc with
listings from the tests of both.