{#- The brand at the header's left: the mark beside the wordmark, linked to the site's
home page, the landing page at `rietx_home` (WP-2021). The top-left logo of a site's
subsite goes to the site's home; the way back to this manual's own front page is the
breadcrumb's first item, "Manual", on every page but that one (`breadcrumbs.html`).
The mark is inline SVG filled from `--accent`, never an ``: an embedded SVG is
its own document, cannot see `html[data-theme]`, and so would follow the system theme
and ignore the toggle (the old manual's `sidebar/brand.html` had the measurement,
mask-image included). Its shapes are a copy of the site's favicon,
`docs/landing/src/favicon.svg`, which `tests/test_manual.py` pins.
`rietx_name` is `_about.DIST_NAME`, handed over through `html_context`. -#}