Match Legacy notebook sparse portrait pages

docs/WRITING_DATA.md

@@ -65,6 +65,13 @@ composition from its page background and symbol-component sheet. Data-pack
 symbols without a bundled resource-pack model use the legacy question-mark
 fallback while keeping their real identifier and display metadata.
 
+The Notebook surface displays pages by their persistent slot index instead of
+packing occupied pages together. Empty positions through the last placed page
+appear darkened. While carrying a Page, all available positions are shown for
+placement. The surface draws the native 30×40 portrait page region from
+Legacy's book UI atlas; symbols are layered at a uniform scale, while the
+square item models remain unchanged in inventories.
+
 ## Ink and baseline link panels
 
 An Ink Vial is crafted from two black dye, a glass bottle, and a water bucket.