Numbered equations¶

Display equations are written once. They render in the Markdown preview (VS Code and JetBrains use KaTeX, GitHub uses MathJax), and the PDF is numbered and cross-referenced by LaTeX.

Classes name the LaTeX environment¶

A class on a display-math block is the name of the LaTeX environment texmark wraps the math in:

Markdown	LaTeX	Result
`$$ x = y $$`	`\[ x = y \]`	unnumbered
`$$ x = y $$ {.equation}`	`\begin{equation} … \end{equation}`	one number
`$$ … $$ {.align}`	`\begin{align} … \end{align}`	one number per row
`$$ … $$ {.gather}`	`\begin{gather} … \end{gather}`	one number
`$$ … $$ {#eq:foo}`	`equation` + `\label{eq:foo}`	numbered, referenceable
`$$ … $$ {#eq:foo .align}`	`align` + `\label{eq:foo}`	per-row, referenceable

A $$…$$ with no class compiles to an unnumbered \[ … \]. A {#eq:foo} label with no class uses the equation environment.

Referencing a numbered equation¶

Label a block with {#eq:foo}, then reference it with @eq:foo or [#](#eq:foo):

$$
\begin{aligned}
\boldsymbol{\mathcal{X}} \sim \mathcal{N}(\bar{X}, \Sigma)
\end{aligned}
$$

{#eq:prior}

The prior is given in @eq:prior — equivalently, [#](#eq:prior).

The eq: prefix resolves to \eqref, a parenthesised, hyperlinked number — "(3)" — where every other prefix produces a bare \ref. See Cross-references for the two reference forms, the full prefix table, and text-carrying links.

Multi-line math and the preview¶

KaTeX cannot render a bare &/\\ inside $$…$$ — multi-line math must be wrapped in aligned to show up in the preview:

$$
\begin{aligned}
a &= b \\
c &= d
\end{aligned}
$$

That previews fine and, untagged, compiles to an unnumbered \[ … \].

For one number over the whole block, tag it {.equation} (or {#eq:foo}). The inner aligned is kept: \begin{equation}\begin{aligned}…\end{aligned}\end{equation} — the canonical idiom for a single-numbered aligned equation.
For one number per row, tag it {.align}. Here texmark strips the inner aligned so the rows land directly in align (otherwise the nesting would collapse back to a single number). You keep the preview and get per-row numbering from the same source. The same unwrapping applies to the rest of the alignment family — flalign, alignat.

This is the only place texmark touches the body; every other environment is wrapped verbatim.

Where to put the trailer (GitHub compatibility)¶

Put the {...} trailer after a blank line, not stuck to the closing $$.

GitHub renders a $$…$$ display block only when the closing $$ ends its line. If the trailer is glued to it ($$ {#eq:foo}), GitHub never sees a valid closing delimiter and the whole equation falls back to literal text. Keeping the delimiters clean and dropping the trailer below a blank line lets the equation render on GitHub and in the VS Code preview:

$$
\begin{aligned}
\boldsymbol{\mathcal{X}} \sim \mathcal{N}(\bar{X}, \Sigma)
\end{aligned}
$$

{#eq:prior}
where $\bar{X}$ is the weighted ensemble mean …

texmark attaches the trailer across any whitespace — same line, the next line, or a blank line — and prose may follow it directly. The blank-line form is the one that also renders on GitHub.

Paragraph flow. The blank line you add before the trailer is only there to satisfy the $$ block syntax, so texmark does not turn it into a paragraph break: the equation, its trailer, and the prose on the trailer's line stay in one paragraph (the equation flows on into the sentence). A new paragraph starts only where you leave a blank line after the trailer's prose — paragraph breaks are controlled by what comes after the {...}, not by the syntactic blank line before it.

$$
\Sigma_{i,j} = \tfrac{1}{M-1}\textstyle\sum_m (X_i^m-\bar X_i)(X_j^m-\bar X_j)
$$

{#eq:cov}
where $\mathcal{L}$ is the localisation kernel.   ← same paragraph as the equation

This sentence starts a new paragraph.             ← blank line above => new paragraph

GitHub and the KaTeX preview show {#eq:prior} as literal text, because the attribute is not part of their Markdown. The equation itself still renders, and the PDF is unaffected.

Caveats¶

The label shows in the preview. Neither KaTeX (VS Code) nor GitHub understands the {#eq:foo} trailer, so it appears as literal text near the rendered equation. The PDF is unaffected. Cosmetic, and only on labelled blocks — see Where to put the trailer.
Unknown environments pass through with a warning. A typo like {.equaton}, or an inner-only environment used standalone like {.aligned} (which errors in LaTeX), is emitted as-is and logged — so a build warning points you at the mistake.
Numbering is LaTeX's. texmark emits \label; the actual numbers come from LaTeX's normal two-pass .aux resolution. Nothing is counted by texmark, so numbering and \eqref behave exactly as in hand-written LaTeX.