Owner direction (2026-09-07): plugin panels need a bigger default size
and real resizability. Plugin markup panels were fixed-size with no way
to opt in to drag-resize, and only <meter> exposed an anchor attribute
(comma-separated, silently dropping unknown tokens) — no other element
could stretch or reposition when its window resized.
<panel resizable="true" minw= minh=> is now the explicit opt-in (default
false — a panel with none of these attributes gets Resizable=false,
ResizeX=false, ResizeY=false, matching every plugin panel shipped today,
e.g. mosstank.xml's resize="none"). resizable="true" arms both axes and
defaults the min size to the authored w/h so a resizable panel never
shrinks below the layout its author tested; the pre-existing resize=
attribute still narrows to one axis on top of that.
anchor="left top right bottom" (space-separated, case-insensitive) now
applies uniformly via ApplyCommon to every element (<group>, <list>,
<menu>, <field>, <label>, <button>, <icon>, plus <meter>/<tab>/<toggle>/
<slider> for free) instead of just <meter>'s own comma-separated,
non-throwing parse. An unknown token now throws FormatException naming
the element, matching this file's "malformed markup throws at Build"
convention everywhere else. No new plumbing is needed for live re-layout
or group-relative child anchoring — UiElement.ApplyAnchor/AnchorEdges
already measure a child's margins against its own direct Parent's
Width/Height every draw, and RetailWindowManager.ResizeTo/UiRoot's
existing edge-drag resize already respect Resizable/ResizeX/ResizeY/
MinWidth/MinHeight generically for any registered window.
Mutation proof: reverted MarkupDocument.cs to its pre-change state and
reran the 25 new MarkupResizableAnchorTests — 17 failed (the anchor
grammar, resizable/minw/minh parsing, live re-layout, and golden-draw
tests), 8 passed trivially (cases asserting the unchanged no-attribute
default). Restoring the implementation turned all 25 green with no
regression in the existing 227 Markup/PluginSidePanel/RetailWindow/
Anchor-filtered tests (252/253, 1 pre-existing unrelated skip).
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
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