Class is not a Page property

[acarum]

mxcli version || mxcli version v0.13.0
Mendix version | | 11.11.0
Scenario | I need to associate a Css class to a page
Expected output | I need to associate a Css class to a page
Experienced output | The Class is not a page property

[ako]

Analysis + fix (implemented in 56f3fea9d)

Root cause: a page does have a CSS class — every Forms$Page carries a Forms$Appearance with Class/Style — but nothing wired it to MDL:

• pages.Page had no Class/Style field, and both writers hardcoded the page appearance empty (Class: "").
• The CREATE PAGE header's generic property branch is IDENTIFIER : value, but Class/Style are reserved lexer tokens (CLASS/STYLE), so they never matched IDENTIFIER → "unknown page property" (unlike PopupWidth, which is a plain identifier).

Fix — page-level Class/Style are now wired through the whole pipeline (same shape as the PopupWidth work in #661/#713):

• Grammar: explicit CLASS/STYLE alternatives in pageHeaderPropertyV3.
• Model/AST/visitor/builder: pages.Page + CreatePageStmtV3 gain Class/Style; the header visitor and page builder populate them.
• Writers: legacy serializePage and modelsdk newAppearance(page.Class, page.Style, …) emit them onto Forms$Appearance.
• DESCRIBE: reads them back into the CREATE PAGE header, so it round-trips.
• ALTER PAGE: SET Class = '…' / SET Style = '…' (page-level, no ON) via the shared applyPageLevelSetMut (both engines; creates the Appearance sub-doc if absent).

Usage

CREATE PAGE MyModule.Home (
  Title: 'Home',
  Layout: Atlas_Core.Atlas_Default,
  Class: 'container-fluid bg-light',
  Style: 'min-height: 100vh'
) { … }

ALTER PAGE MyModule.Home { SET Class = 'container'; SET Style = 'padding: 10px'; };

Verified

End-to-end on both engines (modelsdk default + --engine legacy): CREATE + ALTER set the class/style, describe round-trips them, the BSON Forms$Appearance carries the values, and mx check (11.12.0) = 0 errors. Unit tests added (visitor + pagemutator); bug-test mdl-examples/bug-tests/714-page-class.mdl; syntax help / quick reference / create-page skill updated.

Note: over the MCP/PED backend, page appearance isn't part of the pg LightPage shape (same limitation as Url/pop-up settings for pages), so set the page Class via the local engine or Studio Pro when authoring over MCP.