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Markdown BBCode Mod — Supported Syntax Reference

Generated from MDParser.php's actual implementation as of today's GFM-conformance pass. Every row below is something the parser genuinely handles, not aspirational.

Before posting any part of this document to the forum: SMF has no automatic escaping for text that merely looks like BBCode. A literal [md] typed or pasted into a normal post is a real tag-open, not example text — and since it's registered as unparsed_content, everything after it gets swallowed until a matching `

` (or the rest of the post just disappears into the block). Backticks/code formatting do **not** protect against this — that's a markdown convention, meaningless to SMF's BBC parser, which runs before markdown rendering ever happens. Wrap any literal `

/

` in `[nobbc]...[/nobbc]`, or HTML-entity-encode the brackets (`[md]`), before posting.

> **Forum BBC policy:** all standard BBCode tags are disabled on this forum except **`[nobbc]`** (kept enabled/exempt — it's the escape hatch that makes the warning above possible to follow) and **`

`** itself (the tag this whole document is about). Every other bracket-tag typed in a post is inert, literal text.

Element	Raw source (unrendered)	Rendered output
Heading (ATX)	# H1 … ###### H6	<h1>H1</h1> … <h6>H6</h6>
Heading (Setext)	Title\n===== / Title\n-----	<h1>Title</h1> / <h2>Title</h2>
Bold	**bold** or __bold__	<strong>bold</strong>
Italic	*italic* or _italic_	<em>italic</em>
Bold + italic	***both*** or ___both___	<em><strong>both</strong></em>
Strikethrough	~~struck~~	<del>struck</del>
Inline code	`code`	<code>code</code>
Inline code (contains a backtick)	code with inside` ``	<code>code with inside</code>`
Fenced code block	``php/ code / ` (also~~~`)	<pre class="md-code-block"><code class="language-php">...</code></pre> (the class="language-X" only appears when a language is specified after the fence)
Indented code block	4 spaces or a tab before each line (blank lines inside stay part of the same block)	<pre class="md-code-block"><code>...</code></pre>
Blockquote	> quoted (nested: >> quoted)	<blockquote><p>quoted</p></blockquote>
Unordered list (tight)	- item / * item / + item	<ul><li>item</li></ul>
Unordered list (loose — blank line between items)	- one\n\n- two	<ul><li><p>one</p></li><li><p>two</p></li></ul>
Ordered list	1. item or 1) item	<ol><li>item</li></ol>
Ordered list, custom start	7. item	<ol start="7"><li>item</li></ol>
List marker change starts a new list	- foo\n- bar\n+ baz	two separate <ul> elements (different bullet char = different list)
Ordered list can't interrupt a paragraph unless it starts at 1	Some text\n14. more text	stays one <p>, not a <p> + <ol start="14">
Empty list item (bare marker, nothing after it)	- alone on a line	<ul><li></li></ul>
Link	[text](url "title")	<a href="url" title="title" rel="noopener noreferrer nofollow">text</a>
Link title, alternative delimiters	[text](url 'title') or [text](url (title))	same as above
Link text with nested brackets	[link [foo] bar](url)	<a href="url">link [foo] bar</a>
Link, empty URL	[text]()	<a href="">text</a>
Link, angle-bracket destination (allows spaces)	[text](<my file.pdf>)	<a href="my%20file.pdf">text</a>
Link destination, balanced parens	[text](foo(and(bar)))	<a href="foo(and(bar))">text</a>
Link destination, percent-encoding	[text](foo b&auml;)	<a href="foo%20b%C3%A4">text</a> (HTML entities decoded, then unsafe bytes percent-encoded; existing %XX sequences left alone)
Image		<img src="url" alt="alt" title="title">
Autolink (angle brackets)	<https://example.com> or <user@example.com>	<a href="https://example.com" rel="noopener noreferrer nofollow">https://example.com</a> (mailto autolinks omit rel)
Bare URL autolink (GFM ext.)	plain https://example.com in running text	auto-linked, trailing .,!?: etc. left outside the link
Bare www. autolink (GFM ext.)	plain www.example.com in running text	linked with href="http://www.example.com"
Bare email autolink (GFM ext.)	plain name@example.com in running text	<a href="mailto:name@example.com">name@example.com</a>
Horizontal rule	---, ***, or ___ alone on a line	<hr>
Hard line break	line ending in two trailing spaces	`
`
Paragraph break	blank line between blocks	separate <p> elements
Escaping	0not italic1 — any ASCII punctuation character can be escaped this way, not just markdown-syntax ones	*not italic* (literal)
GFM table	<code>| a | b |

|---|---:| | 1 | 2 |</code> | <table class="md-table"> with style="text-align:right" etc. from the :---/---:/:---: header row |

Forum-specific extensions (not part of GFM)

Element	Raw source (unrendered)	Rendered output
Wikipedia link	{wiki:Article Name}	<a href="https://en.wikipedia.org/wiki/Article_Name" rel="noopener noreferrer nofollow">Article Name</a> — same tab, no target="_blank"

Exclusions & Gaps

Everything the parser doesn't do, grouped by why — because "not spec-complete" covers two very different situations: things we chose not to build, and things security requires us not to build.

Security-motivated exclusions (deliberate — do not "fix" these for conformance)

Excluded	Reason
Raw HTML blocks (multi-line embedded HTML in a post)	The mod's entire security model is "escape everything on input, then selectively re-decode only what's explicitly recognized as markdown syntax." Parsing raw HTML blocks back into the page means accepting arbitrary user-supplied HTML — exactly the attack surface the last external security review closed (the stored-XSS-via-code-span and control-character URL bypass findings). Re-opening this for GFM conformance would undo that work.
Autolinking arbitrary URI schemes (<irc://...>, <made-up-scheme://...>)	isSafeUrl() only allows http, https, ftp, ftps, mailto. CommonMark's actual rule permits any scheme matching [a-zA-Z][a-zA-Z0-9+.-]{1,31}: — a superset that, unfiltered, would also cover javascript:, data:, vbscript:. Broadening the allowlist to add specific safe schemes (irc://, magnet:, etc.) is a legitimate future option, but it's a deliberate allowlist decision to make each time, not something that should get widened automatically in the name of spec coverage.

Scope decisions (no security angle — just low value for a forum)

Excluded	Reason
Reference-style links [text][ref] + [ref]: url	Adds a second-pass resolution step for a syntax forum posters essentially never use
Footnotes	Same reasoning as reference-style links
Task-list checkboxes - [ ]	Low forum-relevance extension

Known remaining gaps (real bugs, still open — no security implication)

• Angle-bracket link destination spanning a literal line break ([link](<foo\nbar>), which per spec should not be a valid link) currently isn't rejected — a structural side-effect of paragraph line-joining happening at the block level before this inline check can see the newline.
• Blockquote laziness inside an already-open non-paragraph block (e.g. an unclosed fenced code block within a > quote) isn't tracked precisely — ordinary paragraph laziness is handled correctly.
• One emphasis test case (__foo, __bar__, baz__) where our output disagrees with the npm commonmark reference package but matches the literal cmark-gfm spec.txt expectation — a documented gray area, not chased further.