(registered 2026-11-13, last updated 2026-11-13)

Identifier: zipdown

Name: Zipdown

Description: Zipdown is Markdown with its images and other files carried inside the same text file. A Zipdown file is a Markdown document followed by a hidden payload: the assets as base64 blocks inside an HTML comment, then an index of each asset's path, size, line range, and SHA-256 hashes, and a short plain-text note. A plain Markdown renderer still shows the document; a Zipdown reader verifies the hashes before showing any asset, and can check an optional Ed25519 signature. Every plain Markdown file is a Zipdown file with no assets. The body's syntax defaults to zd1: CommonMark 0.31.2 with extensions, in practice GFM without raw HTML, plus Zipdown's own marks for text size, highlight, spoilers, color, mentions, indentation, and image size. Unlike Original, raw HTML is never rendered. A header can name another variant from this registry (such as GFM or CommonMark) instead of zd1.

Additional Parameters: None.

Fragment Identifiers: None.

References: https://zd.treeflow.ai/spec/ (current version); https://zd.treeflow.ai/spec/v0.5/ (version 0.5)

Contact Information: Troy Wu <standards&treeflow.ai>