Flatten X4 tables that hold images or nested tables

CrossPoint and CrossInk print an image's alt text instead of drawing it
inside a table cell, and CrossInk drops all text of a nested table.
Layout tables (The Space Review's figures) lost every image on the X4:
59 images across 8 articles in the published issues.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/epub/x4.rs

@@ -136,11 +136,145 @@ pub const CODE_GAP_CLASS: &str = "code-gap";
 /// then soft-hyphenate anything too long for it to wrap (§3.10).
 pub fn simplify_xhtml(xhtml: &str) -> String {
     paragraph_code_lines(&break_long_words(&strip_attributes(
-        xhtml,
+        &flatten_lossy_tables(xhtml),
         DROPPED_ATTRIBUTES,
     )))
 }
 
+/// Table elements dropped outright when an image table is flattened.
+const TABLE_FRAME_ELEMENTS: &[&str] =
+    &["table", "thead", "tbody", "tfoot", "tr", "colgroup", "col"];
+
+/// Table elements whose content becomes a `<div>` when a table is flattened.
+const TABLE_CELL_ELEMENTS: &[&str] = &["td", "th", "caption"];
+
+/// Elements the X4 firmwares treat as images.
+const IMAGE_ELEMENTS: &[&str] = &["img", "image"];
+
+/// Turn every table the X4 firmwares would lose content from into plain
+/// `<div>` blocks: one that holds an image or another table.
+///
+/// The firmwares (CrossPoint and CrossInk) never draw an image inside a table
+/// cell: they print its alt text instead. Publishers that lay out a figure as a
+/// one-cell table with the caption beneath the image (The Space Review, many
+/// older sites) would lose every figure. CrossInk also throws away all the text
+/// of a table nested in another. Flattening keeps each cell's content in order,
+/// which is how the firmwares already fall back for any table they cannot lay
+/// out as a grid. Tables of plain text stay tables.
+fn flatten_lossy_tables(html: &str) -> String {
+    let mut out = String::with_capacity(html.len());
+    let mut cursor = 0usize;
+    while let Some(rel) = html[cursor..].find('<') {
+        let start = cursor + rel;
+        out.push_str(&html[cursor..start]);
+        let Some(end) = tag_end(html, start) else {
+            out.push_str(&html[start..]);
+            return out;
+        };
+        let tag = &html[start..end];
+        if let Some(name) = raw_text_name(tag) {
+            let close = find_close_tag(html, end, name).unwrap_or(html.len());
+            out.push_str(&html[start..close]);
+            cursor = close;
+            continue;
+        }
+        if !is_element_tag(tag, "table", false) {
+            out.push_str(tag);
+            cursor = end;
+            continue;
+        }
+        let table_end = matching_table_end(html, start);
+        let table = &html[start..table_end];
+        // Past the outer `<table` tag, so it doesn't count as its own nesting.
+        let inner = &table[end - start..];
+        if contains_element(inner, IMAGE_ELEMENTS) || contains_element(inner, &["table"]) {
+            out.push_str(&flatten_table(table));
+        } else {
+            out.push_str(table);
+        }
+        cursor = table_end;
+    }
+    out.push_str(&html[cursor..]);
+    out
+}
+
+/// Byte offset just past the `</table>` that closes the table opened at
+/// `start`, counting nested tables; the end of `html` if it is never closed.
+fn matching_table_end(html: &str, start: usize) -> usize {
+    let mut depth = 0usize;
+    let mut cursor = start;
+    while let Some(rel) = html[cursor..].find('<') {
+        let tag_start = cursor + rel;
+        let Some(end) = tag_end(html, tag_start) else {
+            break;
+        };
+        let tag = &html[tag_start..end];
+        if is_element_tag(tag, "table", false) && !tag.ends_with("/>") {
+            depth += 1;
+        } else if is_element_tag(tag, "table", true) {
+            depth = depth.saturating_sub(1);
+            if depth == 0 {
+                return end;
+            }
+        }
+        cursor = end;
+    }
+    html.len()
+}
+
+/// Whether any tag in `html` opens one of the named elements.
+fn contains_element(html: &str, names: &[&str]) -> bool {
+    let mut cursor = 0usize;
+    while let Some(rel) = html[cursor..].find('<') {
+        let start = cursor + rel;
+        let Some(end) = tag_end(html, start) else {
+            return false;
+        };
+        let tag = &html[start..end];
+        if names.iter().any(|name| is_element_tag(tag, name, false)) {
+            return true;
+        }
+        cursor = end;
+    }
+    false
+}
+
+/// Rewrite one table's markup (nested tables included) as `<div>` blocks.
+fn flatten_table(table: &str) -> String {
+    let mut out = String::with_capacity(table.len());
+    let mut cursor = 0usize;
+    while let Some(rel) = table[cursor..].find('<') {
+        let start = cursor + rel;
+        out.push_str(&table[cursor..start]);
+        let Some(end) = tag_end(table, start) else {
+            out.push_str(&table[start..]);
+            return out;
+        };
+        let tag = &table[start..end];
+        cursor = end;
+        let is = |names: &[&str], closing: bool| {
+            names.iter().any(|name| is_element_tag(tag, name, closing))
+        };
+        if is(TABLE_FRAME_ELEMENTS, false) || is(TABLE_FRAME_ELEMENTS, true) {
+            // A newline, not nothing: the firmwares buffer the last word
+            // before an element boundary until whitespace arrives.
+            out.push('\n');
+        } else if is(TABLE_CELL_ELEMENTS, false) {
+            out.push_str(if tag.ends_with("/>") {
+                "<div></div>"
+            } else {
+                "<div>"
+            });
+        } else if is(TABLE_CELL_ELEMENTS, true) {
+            out.push_str("</div>");
+        } else {
+            out.push_str(tag);
+        }
+    }
+    out.push_str(&table[cursor..]);
+    out
+}
+
 /// Turn each line of every `<pre>` into its own `<p class="code-line">`.
 ///
 /// The X4 firmwares (CrossPoint and forks such as CrossInk) ignore
@@ -975,4 +1109,97 @@ mod tests {
             "<?xml version=\"1.0\"?>\n<!DOCTYPE html>\n<html><body><p>2 &lt; 3</p></body></html>";
         assert_eq!(simplify_xhtml(input), input);
     }
+
+    /// Whether any image in `html` sits inside a table, where the X4
+    /// firmwares print its alt text instead of drawing it.
+    fn image_inside_table(html: &str) -> bool {
+        let mut depth = 0usize;
+        let mut cursor = 0usize;
+        while let Some(rel) = html[cursor..].find('<') {
+            let start = cursor + rel;
+            let end = tag_end(html, start).unwrap();
+            let tag = &html[start..end];
+            if is_element_tag(tag, "table", false) {
+                depth += 1;
+            } else if is_element_tag(tag, "table", true) {
+                depth -= 1;
+            } else if depth > 0 && IMAGE_ELEMENTS.iter().any(|n| is_element_tag(tag, n, false)) {
+                return true;
+            }
+            cursor = end;
+        }
+        false
+    }
+
+    #[test]
+    fn a_figure_laid_out_as_a_table_becomes_divs() {
+        // The Space Review's figure markup (issue 2026-10-01).
+        let input = "<p>Before.</p><table><tbody><tr><td><img src=\"images/a.jpg\" alt=\"ELINT images\"/><p>During the 1970s. (credit: NRO)</p></td></tr></tbody></table><h3>Next</h3>";
+        let out = simplify_xhtml(input);
+        assert!(!image_inside_table(&out), "{out}");
+        assert!(!out.contains("<t"), "{out}");
+        assert!(
+            out.contains("<div><img src=\"images/a.jpg\" alt=\"ELINT images\"/><p>During the 1970s. (credit: NRO)</p></div>"),
+            "{out}"
+        );
+        assert!(
+            out.starts_with("<p>Before.</p>") && out.ends_with("<h3>Next</h3>"),
+            "{out}"
+        );
+    }
+
+    #[test]
+    fn every_cell_of_an_image_table_keeps_its_content_in_order() {
+        let input = "<table class=\"x\" width=\"600\"><caption>Cap</caption><thead><tr><th>A</th><th>B</th></tr></thead><tr><td colspan=\"2\"><img src=\"1.jpg\"/></td></tr><tr><td>left</td><td>right</td></tr></table>";
+        let out = flatten_lossy_tables(input);
+        assert_eq!(
+            out.split_whitespace().collect::<String>(),
+            "<div>Cap</div><div>A</div><div>B</div><div><imgsrc=\"1.jpg\"/></div><div>left</div><div>right</div>"
+        );
+    }
+
+    #[test]
+    fn nested_image_tables_flatten_from_the_outside_in() {
+        for input in [
+            // Image in the inner table only.
+            "<table><tr><td><table><tr><td><img src=\"1.jpg\"/></td></tr></table></td></tr></table><p>after</p>",
+            // Image in the outer table after a text-only inner table.
+            "<table><tr><td><table><tr><td>x</td></tr></table><img src=\"1.jpg\"/></td></tr></table><p>after</p>",
+            // An SVG `<image>` counts too.
+            "<table><tr><td><svg><image href=\"1.jpg\"/></svg></td></tr></table><p>after</p>",
+        ] {
+            let out = simplify_xhtml(input);
+            assert!(!image_inside_table(&out), "{out}");
+            assert!(!out.contains("<table"), "{out}");
+            assert!(out.ends_with("<p>after</p>"), "{out}");
+        }
+    }
+
+    #[test]
+    fn a_nested_text_table_flattens_its_outer_table() {
+        let input = "<table><tr><td>outer<table><tr><td>inner</td></tr></table></td></tr></table>";
+        let out = flatten_lossy_tables(input);
+        assert_eq!(
+            out.split_whitespace().collect::<String>(),
+            "<div>outer<div>inner</div></div>"
+        );
+    }
+
+    #[test]
+    fn text_tables_stay_tables() {
+        let input = "<table><tr><th>Year</th><td>1971</td></tr></table><p><img src=\"1.jpg\"/></p><table><tr><td>2</td></tr></table>";
+        assert_eq!(flatten_lossy_tables(input), input);
+    }
+
+    #[test]
+    fn table_markup_inside_raw_text_is_left_alone() {
+        let input = "<script>let t = '<table><td><img src=x></td></table>';</script>";
+        assert_eq!(flatten_lossy_tables(input), input);
+    }
+
+    #[test]
+    fn an_unclosed_image_table_still_flattens() {
+        let out = flatten_lossy_tables("<table><tr><td><img src=\"1.jpg\"/>");
+        assert!(!image_inside_table(&out), "{out}");
+    }
 }