Morph the rail's FAB, and offer a divider, no fill and a width floor

M3 asks the rail to animate its FAB into an extended FAB as it expands; the
documented pattern was two FABs swapped by `display`, so the collapsed one
appeared at once while the rail's width was still springing. The header now takes
one <x-fab label icon> whose label springs open and shut on the rail's own
spring — and names it at both widths, where the collapsed FAB had needed a
tooltip to have a name at all.

M3 also lists two container treatments as optional that the library had neither
of: `divider` draws the vertical divider on the page's edge, which is its own
answer to a page scrolling under a fixed rail, and `fill="false"` drops the
container colour. Neither reaches a rail open over a scrim. And a `collapsible`
rail, whose width is the visitor's choice rather than the window's, is held to
the collapsed 96px below `medium`, where M3 asks for a navigation bar instead.
Plan: docs/plans/material-3-alignment.md, step 21 (navigation N-22, N-23, N-24).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9
This commit is contained in:
Andreas Reinhold / reini
2026-09-14 06:16:37 +02:00
co-authored by Claude Opus 5
parent 1218371568
commit 7d14f2bd03
7 changed files with 114 additions and 29 deletions
@@ -47,8 +47,9 @@
Slots, each rendered once: `banner` (a bar across the whole window, above the rail and the
page — M3's scaffold is bars, then rails, then panes), `brand` (beside the rail's menu button
while it is expanded), `rail-header` (under it: a FAB — see `<x-navigation-rail>` for its two
shapes), `rail-footer` (at the foot of the rail: footer destinations, an account), `actions`
while it is expanded), `rail-header` (under it: one `<x-fab label="…" icon="…">`, which the
rail morphs between a FAB and an extended FAB as it opens), `rail-footer` (at the foot of the
rail: footer destinations, an account), `actions`
(a row of icon buttons at the very foot, stacked when the rail is collapsed: a theme toggle,
sign out), `top` (the page's own bar, above the page and *beside* the rail) and the page
itself. The rail is one element at every width, so what is in it is also in the modal rail a