` even in Arial (TL Community News), and centered multi-line system-font `` marketing copy (Pi-hole). Wide left-aligned system-font article prose (HN / Wikipedia) stays structured Text.
**Multi-line `
` / `white-space:pre*`:** leaf extract used to collapse all whitespace (`/\s+/g` → space), so indented code became one soft-wrapped line and Gum broke mid-token (`new` / `Foo();` on tabsoverspaces). Prefer baking multi-line preformatted hosts (`shouldRasterTextHeavyCell` on `` or phrasing-only pre hosts, counting distinct client-rect Ys — not raw rect count, or pastebin highlighter spans false-trigger). When structured, `textForWhiteSpace` must preserve newlines/spaces for `pre` / `pre-wrap` / `break-spaces` / `pre-line`.
**Font Awesome / icon-font `::before`:** glyphs use `content:"\uf0xx"` with `width/height:auto` (no border/bg box). `needsRasterPaint` must treat icon-font families and Private Use Area content as pseudo chrome — otherwise Gum draws empty bordered squares (Embrace the Red header social icons).
**Empty-content pseudo backdrops:** overlays often use `::before { content:""; inset:0; background:…; opacity:… }` (Pi-hole hero tint). Do not discard the pseudo because its unquoted content is empty. Bake the host chrome (background + pseudo) while hiding descendants so nav/text remain structured; icon/glyph pseudos still bake the whole host.
**Transparent inline SVG rasterization:** Playwright `omitBackground` clears the page canvas but still captures painted DOM ancestors through transparent SVG pixels. Isolate the SVG by temporarily neutralizing ancestor chrome and hiding sibling branches (`raster-isolation.ts`), then restore exact inline styles. Otherwise a separator SVG over a photo bakes the photo and Gum paints a duplicate strip (Pi-hole hero). **Path indices must match extract** — skip `SCRIPT`/`STYLE`/`NOSCRIPT`/… the same way `extractBoxTree` does; Chromium may treat `NOSCRIPT` as visible, so body path `[0]` would hit it while extract's `[0]` is the app root (catfishing.net nav icons fell back to opaque page clips). Pin `color` on the target before clearing ancestors so `currentColor` fills survive (do not pin `-webkit-text-fill-color` on text hosts — it flattens descendant span colors). `clearInheritedColor:false` is available for future text-heavy transparent rasters; opaque text-heavy cells remain the default until Gum Sprite alpha compositing matches Chromium for those plates.
**Google Fonts unicode-range subsets:** each weight has many `@font-face` rules (Latin / Latin-ext / Cyrillic / …). Picking the first CSS match often bakes a Cyrillic-only TTF → empty KernSmith atlas → Arial fallback. Prefer faces whose `unicode-range` covers basic Latin (`unicodeRangeCoversBasicLatin`); reject baked TTFs that lack `A`/`a`/`M`/`m` and try the next URL.
**Empty custom FontCache atlases:** some web `.ttf` bakes (e.g. Poppins Light) yield `chars count=2` (space only) → invisible text. `repairEmptyCustomFonts` in `fonts.ts` rewrites those `Font=Fonts/….ttf` refs to Arial and re-bakes. Do not chase “missing text” with layout probes until you’ve checked `FontCache/*.fnt` `chars count`.
**Mac-only faces on Windows:** `Menlo` / `Monaco` / `Helvetica Neue` resolve via `FACE_ALIASES` to Consolas / Arial so gumcli can embed them.
**Bad font downloads:** `@font-face` URLs can return HTML/empty bytes. `looksLikeFontBuffer` + multi-URL retry in `materializeWebFonts` skip non-sfnt/woff payloads and try the next candidate (KORE Proxima Nova w400).
**White canvas default:** browsers paint the page canvas white when neither `` nor `` sets an opaque background (CSS "canvas"). Gum has no such default → the root stays transparent and the screenshot is transparent (RGB 0,0,0 under alpha 0) where Chromium is white; the diff scores every such pixel as a full miss (OWASP content band was ~40% alone). `extractBoxTree` propagates the effective page background (html → body → white) onto the root `body`/`html` node so `BodyBg` paints a backmost fill. Only fires when the root is body/html with a transparent bg and no background-image (Space Jam's opaque/starfield body is untouched).
**Negative root `y` clip height:** sticky chrome can make `body.getBoundingClientRect().y` negative (mdbook / Rust book ≈ -50). Clamping only the clip origin to 0 while keeping the full measured height captures white canvas *below* where Gum's BodyBg ends (~7% false miss). Chromium shot + gum align must use root∩viewport (`intersectScreenshotClip`): `y1 = ceil(y+h)`, not `h` after clamping `y`.
**Out-of-flow descendants inflating a backdrop:** `backdropHeight`/`textOverflowPad` walk a styled container's subtree to pad for BitmapFont spill. A `position:fixed`/`absolute` descendant (e.g. a cookie banner nested in ``, painted at `y=800`) would stretch the header's painted backdrop from ~159px to ~1544px and tint the whole page with the header color (OWASP `#disclaimer-container`). `textOverflowPad` skips out-of-flow subtrees — they paint at their own coordinates and are not part of an ancestor's content box.
**Negative z-index abs under flex/grid:** CSS paints `z-index < 0` absolutes *before* in-flow content. Gum paints siblings in instance order, so a watermark abs (`z-index: -10`) emitted after `*Content` covers the nav (catfishing.net). Emit negative-z abs onto the outer box *before* creating `*Content`, then in-flow into Content, then `z-index >= 0` abs after.
**Nested fixed cookie banners:** `stabilizeDynamicMedia` hides GDPR toasts so fidelity measures page chrome, not consent UI. Match by id/class *and* by cookie-copy text on **any** `position:fixed`/`sticky` node — not only `body > *`. OWASP nests `#disclaimer-container` under ``; a body-direct scan never sees it (~3% of the residual gate).
**System font stacks:** CSS `-apple-system, BlinkMacSystemFont, "Segoe UI", …` must resolve via `resolveCssFontFamily` to `Segoe UI` (not the synthetic first token). Otherwise Gum falls back to Arial while Chromium on Windows uses Segoe.
**Hidden-menu `textContent` on custom hosts:** when every element child is `display:none` (closed language ``, collapsed mega-menu), `elementChildren` is empty and the host was treated as a text leaf using `textContent` — which still concatenates those labels. Gum then paints "English Deutsch…" over the header (web.dev). Use `innerText` for that leaf path so paint-hidden descendants stay out of the string.
**CSS `mask-image` icons:** UnoCSS / Iconify (`i-mdi:*`) paint a solid `background-color` cut by `mask-image` SVG data URLs — not `` and not `::before`. Detect mask/webkit-mask ≠ none → `needsRaster` + omit background, or Gum draws solid squares (crates.io theme / search / stats icons).
**`.sr-only` / visually-hidden:** 1×1 + `overflow:hidden` (or `clip-path: inset(50%)`) still passes opacity/display checks. Skip in `isVisible` or aria labels leak as painted text (crates.io "Change color scheme…", Search).
**Text sibling next to non-phrasing kids:** element-only walks drop `#text` next to `` (crates.io brand "crates.io"). When a host has nonempty text siblings, walk `childNodes` like the phrasing path.
**`display:contents`:** generates no CSS box — flatten so children participate in the parent's flex/grid (crates.io brand logo stacked under title when `` stayed a 0×0 flex item). Skip `` (never paints).
**Pseudo glyph content:** `::after { content: "▼" }` has no width/height/bg — still needs raster (crates.io Menu caret). Treat nonempty pseudo `content` as chrome.
**Pill `border-radius: 9999px`:** CSS clamps to half the shorter side; Gum `CornerRadius` does not. Clamp extracted radius to `min(w,h)/2`. Near-pill hosts (`r ≥ 40%` of min side) still need raster — gumcli filled rectangles often stay sharp, and baking also captures `::placeholder` (crates.io search).
**Custom-font multi-line `` prose:** `shouldRasterTextHeavyCell` covered `P`/`H*`/`A`/`LI` but crates.io hero copy is a leaf `
` in Fira Sans. Include leaf-like custom-font DIVs (not system faces, not layout wrappers with block kids). Large single-line custom-font `H*` (≥24px) and leaf `SPAN`/`DIV` (≥28px) also bake — KernSmith AA/weight still misses Chromium without wrap (crates.io title + download counts).
**Custom-font data `
`:** short Oxygen/etc cells (dates, version links) each miss BitmapFont AA; baking every `TD` is noisy. Raster substantial custom-font tables (`≥200×80`, enough text) as one sprite (kernel.org releases).
**Open nav flyouts:** `stabilizeDynamicMedia` collapses `details[open]`, `aria-expanded=true` (+ `aria-controls` panels), absolute/fixed `[role=listbox|menu]`, and presses Escape so resting chrome is measured.
**Percent-encoded `data:image/svg+xml`:** select chevrons etc. need `parseDataImageUrl` (`decodeURIComponent`) — the old `;base64`-only regex dropped charset URLs (Pocket).
**`