Builtins are chips that link to a glossary generated from the registry, and the virtual filesystem is drawn as a tree

#word draws a builtin as a chip on the tag's ground over a rule (Look and
Exec in acme's look green and exec red), a <code class="word"> in HTML,
and links it to its entry in a new Builtins chapter wherever that
chapter is in the same output (the book, the site). The chapter is
drawn from docs/typ/builtins-tty.json and builtins-gui.json, which
`zig build builtins-json -Dplatform=tty|gui` writes from the registry
and the Help rows (src/builtins_json.zig, tools/gen_builtins_json.zig;
summaryOf in ninep/ctl.zig is now pub); style.typ merges them, marking
the window-only words. The doc steps refresh their build's file first,
and each build's unit-test fails when its file is stale. Everyday words
first (`everyday` in style.typ), then groups by leader prefix as Help
has them, then settings, the words with no path, debugging and
internals, and last an A-Z index of every word. `zig build book` joins
the doc steps.

#fstree draws a directory tree with its connectors, a description
column and links to the sections that document each file; reference.typ
draws the served tree with it, each pane, pty and column file on its
own line, and a test in config.zig checks it against ninep/tree.zig's
files both ways. The cheatsheet has a two-level version. On the site
the tree reads as `tree` text in w3m and wraps descriptions under the
names on a phone.

The site's tutor draws its B1, B2, B3 and 1-2 chords as mouse glyphs;
the landing credits Plan 9 and acme, as does the book's title page;
install.typ no longer lists the mirrors (the footer does).

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 4 insertions, 0 deletions

diff --git a/docs/typ/book.typ b/docs/typ/book.typ
index 7223ea1d..b2245372 100644
--- a/docs/typ/book.typ
+++ b/docs/typ/book.typ
@@ -30,6 +30,10 @@
   text(size: 34pt, weight: "bold", fill: palette.tag-name)[pardes]
   v(4mm)
   text(size: 13pt, style: "italic", fill: palette.tag-fg, tagline)
+  v(10mm)
+  text(size: 11pt, fill: palette.ink)[Built on ideas from #link("https://9p.io/plan9/")[Plan 9] from Bell
+    Labs: #link("https://9p.io/sys/doc/acme/acme.html")[acme]'s text as the interface, and the 9P
+    protocol.]
   v(2fr)
 })