Book formatting fixes.

WIP.md

@@ -499,7 +499,7 @@ Ranked by estimated wall-clock saving on the current Windows machine:
    | `Liquid::Variable#render` total | 10.05 s | 8.96 s | -1.09 s |
 
    The `BlockBody#render` / `Context#stack` / `Variable#render` drops reflect the eliminated `{%- assign -%}` / `{%- if -%}` blocks in head_seo.html (dropped from ~85 lines of Liquid logic to ~20 lines of straight output). The 128 remaining `markdownify` calls come from `book.html`'s part subtitle/intro (~24) and `book-chapter-body.html`'s per-chapter `chapter.content | markdownify` (~100 chapters whose content doesn't start with `<`); both candidates for a follow-up pass (see #3). New `Jekyll::SeoPrecompute#absolute_url` adds 0.44 s for 846 calls, replacing 1,675 filter calls that totalled 0.40 s -- essentially flat, but the absolute_url filter had its own per-build cache, so the swap is a wash on this axis. Output byte-identical to baseline (`diff -rq` clean on all three of `_site/`, `_site-offline/`, `_site-pdf/`).
-3. **`book-chapter-body.html` heading-shift + anchor-prefix `replace` chain → Ruby pass. [LANDED]** Replaced the per-chapter chain of 0-3 heading-shift cascades (12 replaces each), the 12-pattern whitespace span wrapping, and the 13-replace anchor-id prefix pass with a single Liquid filter `book_chapter_transform` (`_plugins/book-chapter-transform.rb`). The filter takes the body, the site baseurl, a precomputed `heading_shift_n` (0-3, derived in Liquid from `skip_base_heading_shift` / `is_sub_page` / `extra_heading_shift`), and the chapter anchor; does all six passes in one method with no intermediate string allocations beyond what the regex engine produces internally. The dead `p1_search` / `p1_replace` / ... whitespace-pattern declarations were also removed from `book.html`'s prologue.
+3. **`book-chapter-body.html` heading-shift + anchor-prefix `replace` chain → Ruby pass. [LANDED]** Replaced the per-chapter chain of 0-3 heading-shift cascades (12 replaces each), the 12-pattern whitespace span wrapping, and the 13-replace anchor-id prefix pass with a single Liquid filter `book_chapter_transform` (`_plugins/book-chapter-transform.rb`). The filter takes the body, the site baseurl, a precomputed `heading_shift_n` (0-3, derived in Liquid from `skip_base_heading_shift` / `is_sub_page` / `extra_heading_shift`), and the chapter anchor; does all seven passes in one method with no intermediate string allocations beyond what the regex engine produces internally (the seventh pass, added later, strips `<details>`/`<summary>` tags so collapsible sections like the FAQ render as flat content in the PDF). The dead `p1_search` / `p1_replace` / ... whitespace-pattern declarations were also removed from `book.html`'s prologue.
 
    The single-pass heading shift (one regex bumping each level by N, capping at h7-stub for source levels above 6) is equivalent to N applications of the bottom-up cascade chain -- each source heading lands at `level + N` or `h7-stub` regardless of how many sequential passes the chain ran, since the cascade structure was an artifact of Liquid not having a bump-by-N primitive, not a semantic requirement.
 

docs/_includes/book-chapter-body.html

@@ -151,7 +151,7 @@
     overrides the class (front-matter, part-foreword), the override
     is used as-is and sub-page styling never kicks in. Otherwise
     sub-pages get the " sub-chapter" suffix and a compound running
-    header ("Module - Member" / "Class.Member").
+    header ("Parent - Member").
   {%- endcomment -%}
   {%- if include.article_class_override -%}
     {%- assign article_class = include.article_class_override -%}
@@ -160,12 +160,7 @@
     {%- assign article_class = 'page' -%}
     {%- if is_sub_page -%}
       {%- assign article_class = article_class | append: ' sub-chapter' -%}
-      {%- if current_index_kind == 'module' -%}
-        {%- assign compound_sep = ' - ' -%}
-      {%- else -%}
-        {%- assign compound_sep = '.' -%}
-      {%- endif -%}
-      {%- assign header_title = current_index_name | append: compound_sep | append: include.chapter.title -%}
+      {%- assign header_title = current_index_name | append: ' - ' | append: include.chapter.title -%}
     {%- else -%}
       {%- assign header_title = include.chapter.title -%}
     {%- endif -%}

docs/_plugins/book-chapter-transform.rb

@@ -28,22 +28,26 @@
 # === Approach ===
 #
 # `book_chapter_transform(body, baseurl, heading_shift_n, chapter_anchor)`
-# does all six passes in one method:
+# does all seven passes in one method:
 #
 #   * Step 1 uses a single literal `gsub!` keyed on the live
 #     `site.baseurl` value (passed as the second filter argument so
 #     the constant isn't baked into the plugin at load time).
-#   * Step 2 walks a frozen `WHITESPACE_PATTERNS` table of 12
+#   * Step 2 strips `<details>`, `</details>`, `<summary>`, and
+#     `</summary>` tags so collapsible sections (FAQ) render as
+#     flat content in the PDF.
+#   * Step 3 walks a frozen `WHITESPACE_PATTERNS` table of 12
 #     literal `[search, replacement]` pairs and applies them in
 #     longest-first order, matching the Liquid chain's order
 #     exactly. Literal `gsub!` on each.
-#   * Steps 3-5 collapse into a single regex pass keyed on
-#     `heading_shift_n` (= 0, 1, 2, or 3 -- precomputed in Liquid
-#     from `skip_base_heading_shift`, `is_sub_page`, and
-#     `extra_heading_shift`). The N-pass cascade of the Liquid
-#     chain is equivalent to a one-pass regex that bumps each
-#     heading level by N, capping at `h7-stub` for levels above 6.
-#   * Step 6 replaces the 13 literal `replace` calls with one regex
+#   * Steps 4 collapses the three heading-shift cascades into a
+#     single regex pass keyed on `heading_shift_n` (= 0, 1, 2, or
+#     3 -- precomputed in Liquid from `skip_base_heading_shift`,
+#     `is_sub_page`, and `extra_heading_shift`). The N-pass cascade
+#     of the Liquid chain is equivalent to a one-pass regex that
+#     bumps each heading level by N, capping at `h7-stub` for
+#     levels above 6.
+#   * Step 5 replaces the 13 literal `replace` calls with one regex
 #     for heading-id injection (matches `<h[2-6]` and `<h7-stub`,
 #     with and without `class="no_toc"`) and one literal `gsub!`
 #     for `href="#`.
@@ -121,6 +125,14 @@ module BookChapterTransform
     # Heading-shift regex. Captures the optional `/` for closing
     # tags and the level digit (1..6). The `\b` after the digit
     # prevents accidental matches on hypothetical `<h12...>`.
+    # <details>/<summary> unwrapping regexes. The FAQ (and potentially
+    # other pages) uses collapsible sections that must read as flat
+    # content in the PDF -- Chromium's internal <details> mechanism
+    # can't be overridden with CSS alone.
+    DETAILS_OPEN_RE  = %r{<details[^>]*>\n?}i.freeze
+    DETAILS_CLOSE_RE = %r{</details>\n?}i.freeze
+    SUMMARY_RE       = %r{<summary[^>]*>|</summary>\n?}i.freeze
+
     HEADING_SHIFT_RE = /<(\/?)h([1-6])\b/.freeze
 
     # Heading-id prefix regex. Matches both `<h[2-6]` and
@@ -137,12 +149,17 @@ def book_chapter_transform(body, baseurl, heading_shift_n, chapter_anchor)
       strip = %(src="#{baseurl}/)
       result.gsub!(strip, %(src=")) if result.include?(strip)
 
-      # Step 2: whitespace span wrapping.
+      # Step 2: unwrap <details>/<summary> for print layout.
+      result.gsub!(DETAILS_OPEN_RE, "")
+      result.gsub!(DETAILS_CLOSE_RE, "")
+      result.gsub!(SUMMARY_RE, "")
+
+      # Step 3: whitespace span wrapping.
       WHITESPACE_PATTERNS.each do |search, replacement|
         result.gsub!(search, replacement)
       end
 
-      # Step 3: heading shift cascade by N levels (0..3).
+      # Step 4: heading shift cascade by N levels (0..3).
       n = heading_shift_n.to_i
       if n > 0
         result.gsub!(HEADING_SHIFT_RE) do
@@ -153,7 +170,7 @@ def book_chapter_transform(body, baseurl, heading_shift_n, chapter_anchor)
         end
       end
 
-      # Step 4: anchor-id prefix on every heading id + intra-chapter href.
+      # Step 5: anchor-id prefix on every heading id + intra-chapter href.
       if chapter_anchor && !chapter_anchor.to_s.empty?
         prefix = "#{chapter_anchor}-"
         result.gsub!(HEADING_ID_RE) do

docs/assets/css/print.css

@@ -13,14 +13,15 @@
   margin: 22mm 20mm 22mm 20mm;
 
   @bottom-right {
-    /* Reads a JS-tracked page number set on each .pagedjs_page wrapper
-       by the Counters handler in docs/lib/paged.browser.js. Switched off
-       `counter(page)` because the aggressive-detach render optimization
-       (perf/detach-pages.js) physically removes finalized pages from the
-       DOM, which breaks CSS counter accumulation. The Counters handler
-       honours the same part-divider counter-reset rules as the original
-       counter(page) did, so part-restarts continue to work. */
-    content: var(--page-num);
+    /* Page number with part-title prefix. `string(part-title)` is set by
+       a hidden span on each part-divider article and persists across
+       pages until the next part. `var(--page-num)` is a JS-tracked
+       counter that survives aggressive-detach (perf/detach-pages.js) --
+       CSS `counter(page)` breaks when finalized pages are removed from
+       the DOM, so the Counters handler polyfills it as a CSS variable.
+       Named @page overrides (front-matter, divider, :first) suppress or
+       simplify this for pages that shouldn't show the part prefix. */
+    content: string(part-title) " - " var(--page-num);
     font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif;
     font-size: 9pt;
     color: #555;
@@ -61,7 +62,7 @@ article {
    + class-restricted selectors on h2/h3 left some top-level chapter
    pages with stale or empty running headers. For top-level chapters the
    span carries the chapter title; for sub-pages it carries the compound
-   "Parent.Sub" / "Parent - Sub" title (1.6c). */
+   "Parent - Sub" title (1.6c). */
 article.page > .header-string {
   string-set: chapter-title content();
   position: absolute;
@@ -71,6 +72,19 @@ article.page > .header-string {
   overflow: hidden;
 }
 
+/* Part-title source for the @bottom-right page number prefix. Each part
+   divider emits a hidden <span class="part-title-string"> carrying the
+   part's title. `string(part-title)` persists across pages until the
+   next part divider overrides it -- same mechanism as chapter-title. */
+article.part-divider > .part-title-string {
+  string-set: part-title content();
+  position: absolute;
+  font-size: 0;
+  width: 0;
+  height: 0;
+  overflow: hidden;
+}
+
 /* ---- Title page (front matter, page 1) ------------------------------
    Emitted by book.html as the first element in <body>, so it lands on
    page 1 without any forced break. Chrome (running header + page number)
@@ -191,7 +205,8 @@ article.front-matter {
 }
 
 @page front-matter {
-  @top-right { content: ""; }
+  @top-right    { content: ""; }
+  @bottom-right { content: var(--page-num); }
 }
 
 

docs/book.html

@@ -100,6 +100,7 @@ <h1 class="book-title">twinBASIC Documentation</h1>
 
 {%- for part in site.data.book.parts -%}
 <article class="part-divider{% if part.no_outline_entry %} silent{% endif %}" id="pt-{{ forloop.index }}">
+  <span class="part-title-string">{{ part.title }}</span>
   <p class="part-number">Part {{ roman[forloop.index0] }}</p>
 {%- if part.no_outline_entry %}
   <p class="part-title-silent">{{ part.title }}</p>

docs/lib/paged.browser.js

@@ -32071,10 +32071,20 @@
 
 				}
 
-				fragment.style.setProperty(`--pagedjs-string-first-${name}`, `"${cleanPseudoContent(varFirst)}`);
-				fragment.style.setProperty(`--pagedjs-string-last-${name}`, `"${cleanPseudoContent(varLast)}`);
-				fragment.style.setProperty(`--pagedjs-string-start-${name}`, `"${cleanPseudoContent(varStart)}`);
-				fragment.style.setProperty(`--pagedjs-string-first-except-${name}`, `"${cleanPseudoContent(varFirstExcept)}`);
+				// Local patch: trailing `"` on each value. Upstream pagedjs
+				// writes `"${...}` (no closing quote); CSS auto-closes
+				// unterminated strings at the declaration boundary, so
+				// `content: var(--pagedjs-string-first-X)` alone works.
+				// But mixing `string()` with other values (e.g.
+				// `content: string(X) " - " var(--page-num)`) breaks --
+				// the substituted `"value` swallows the literal `" - "`
+				// as part of its unterminated string and the browser
+				// drops the declaration. Closing the quote here makes
+				// `string()` composable with sibling content values.
+				fragment.style.setProperty(`--pagedjs-string-first-${name}`, `"${cleanPseudoContent(varFirst)}"`);
+				fragment.style.setProperty(`--pagedjs-string-last-${name}`, `"${cleanPseudoContent(varLast)}"`);
+				fragment.style.setProperty(`--pagedjs-string-start-${name}`, `"${cleanPseudoContent(varStart)}"`);
+				fragment.style.setProperty(`--pagedjs-string-first-except-${name}`, `"${cleanPseudoContent(varFirstExcept)}"`);
 
 
 			}