Convert an existing DOM to Markdown through a small read-only interface. This is an independent implementation with no runtime dependencies, HTML parser, or intermediate DOM. moli-dom::native::NativeDom implements the interface directly.

let root = dom.body_node_id().unwrap_or(dom.document_node_id());
let markdown = moli_html2md::Converter::new(moli_html2md::Options {
    max_depth: 1000,
    default_code_language: Some("text".to_owned()),
    ..Default::default()
})
.convert(&dom, root);

DOM interface

Implement Dom with a copyable node ID and four borrowed queries:

node_kind: document/fragment, lowercase element tag, decoded text, or ignored node.
first_child and next_sibling: ordered traversal of a stable, acyclic tree.
attribute: decoded attribute value, borrowed from the DOM.

The converter does not need parent pointers, mutable access, serialization, or an allocation for each node. The caller chooses the root; its siblings are not visited. Other nodes and their subtrees are ignored. Unknown elements expose their children as ordinary content. Comments and doctypes produce no output.

State machine

A heap task stack tracks node entry, sibling continuation, and element exit. Traversal stores one continuation per level instead of collecting all children.
An inline writer tracks desired and emitted styles, pending whitespace, and block boundaries. It collapses HTML whitespace across node boundaries, keeps Unicode spaces, and coalesces adjacent identical emphasis without changing nodes.
Lists, quotes, headings, and table cells have output buffers finalized by exit tasks. Raw code text uses the same iterative traversal with formatting disabled.
Tables inspect their direct sections, rows and cells before conversion. Nested content uses the task stack; eligibility checks never rescan cell descendants.
Finished blocks and table cells form an owned fragment tree. Fallback joins and writes to parent buffers move fragment roots without copying descendant text; the final output is flattened in one iterative pass. Fragment destruction is iterative too. Quotes, headings and list items still materialize their captured text when rewriting its lines.
List spacing follows block boundaries recorded during conversion. Nested lists keep their own spacing; list items need no preliminary DOM scan.
Ordered lists use start followed by sequential numbers, like Turndown core. reversed and individual li[value] attributes are not represented.
Code fences are chosen after collecting the code text. Language names retain punctuation and Unicode; a name containing backticks uses a tilde fence. Fallback language hints end at the first line ending.

Simple tables produce GFM pipe tables by default. A first row inside thead or consisting entirely of th cells is used as the heading, following the heading recognition used by Turndown's GFM tables plugin. Without a heading, the converter adds an empty heading as wide as the widest data row and retains every data row. Whitespace, comments and empty spacer rows do not affect recognition. The first cell in each column supplies its align attribute; a preceding caption remains a separate Markdown block.

Cells retain inline formatting, links, images and code. Literal pipes are escaped, and cell line breaks and paragraph boundaries use inline <br> tags. Attribute newlines are encoded or normalized so they cannot break a table row. GFM supplies missing trailing cells in short rows; the converter does not allocate a padded grid.

Tables with role="presentation" or role="none" retain ordinary block expansion, in DOM order with blank lines between cells, even when structurally simple. Role matching ignores ASCII case and surrounding HTML whitespace. The same fallback applies to complex tables: non-unit spans, multiple thead rows, rows wider than an explicit header, or cells containing nested tables, lists, headings, quotes or preformatted blocks. Inner simple tables can still produce GFM when their containing layout table is expanded. Other roles, borders and CSS do not select another conversion path. Complex layouts remain readable blocks instead of raw HTML tables.

Supported output includes headings, paragraphs, emphasis, strikethrough, links, images, lists, blockquotes, hard breaks, and fenced code. Inline HTML is used when Markdown delimiters cannot express an emphasis boundary. Script/style/head/noscript/template subtrees are omitted.

max_depth counts the supplied root as depth zero; nodes at or beyond the limit are omitted. All traversal paths, including raw code, use this limit.

preformatted_code preserves whitespace inside inline code when enabled. Its default is false, which collapses ordinary HTML whitespace and moves boundary spaces outside code delimiters. Fenced blocks always preserve nonempty code's spaces and blank lines. Empty blocks still separate surrounding text.

This is a structural content dump. It does not evaluate CSS, visibility, layout, or JavaScript, and cannot preserve all HTML presentation (for example, arbitrary ordered-list numbering or table spanning). DOM snapshots used by Moli's optional strip/base/frame transformations remain the responsibility of the caller.

Verification

cargo test -p moli-html2md covers an independent arena DOM, immutability, whitespace, escaping, code, tables, depth limits, and 20,000 nested nodes on a 64 KiB thread stack. The Turndown differential suite pins 147 upstream fixtures and 50 additional cases. It compares rendered meaning, checks DOM immutability, and explicitly asserts 12 documented differences that preserve Moli's handling of literal text, code, emphasis, and list boundaries. Targeted regressions also cover empty elements, links, attributes in headings and tables, code whitespace and language names, list numbering, and loose lists. An operation-count regression checks nested table fallback at 64, 128 and 256 levels with 256 text bytes per level, both with and without headers. It bounds bytes copied during fragment materialization by output size; completed blocks move into parent buffers without copying their text. A repeated flatten/copy regression fails without timing thresholds. Dropping 20,000 nested fragments is also tested on a 64 KiB thread stack. Emphasis tests cover adjacent links that can use Markdown delimiters and intraword link boundaries that still require inline HTML.

The HTML parser, reference JSON reader, and pulldown-cmark renderer are all test-only dependencies. Tests use checked-in reference outputs and require neither Node nor network access. NativeDom integration and real HTML fixtures are tested in moli-renderer-v8.