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§7.1

Text Formatting Conventions

Which exact markup does each inline mark use?

✅ NormativeSettled. The requirement holds as written.📄 Page ruleCan be applied from the page alone.Read §7.1 in the RFC ↗

The requirement

Inline marks MUST be written with exactly the markup in the table below. Where Markdown has no syntax for a mark, the output MUST use the HTML element named here and MUST NOT use a notation of its own.

When it applies

This is the inline-markup table for the whole protocol. Each row states its requirement; the linked rule holds the detail, the sub-cases and the examples.

Printed mark Requirement Rule
Maths, inline or displayed MUST be LaTeX inside $$ … $$; single $ delimiters MUST NOT be used Inline Equations (§7.2.6), Displayed Equations (§7.2.2)
Hyperlink or email address MUST be raw text by default; link syntax MAY be used only when link extraction was requested Links (§7.2.8)
Bold / italic MUST be Markdown **bold** / *italic*, and only where the glyphs are heavier or slanted Bold and Italics (§7.2.1)
Underline MUST be <u>…</u> Underlined Text (§7.2.12)
Strikeout MUST be ~~…~~ over exactly the struck glyphs Struck and Replaced Values (§9.6.7)
Superscript / subscript MUST be <sup>…</sup> / <sub>…</sub>, never a Unicode raised or lowered glyph Superscript and Subscript (§7.2.11)
Highlight MUST be <mark>…</mark> over exactly the highlighted run Highlighted Text (§7.2.5)
Highlight colour MUST be carried as style="background-color: HTML_COLOR_NAME" on the <mark>, using the nearest HTML colour name Highlighted Text (§7.2.5), Text Colors (§7.3.12)
Text colour, when it is the only distinguisher MUST be <font color="HTML_COLOR_NAME">…</font> Text Colors (§7.3.12)
Signature MUST be [signature:{name}], or bare [signature] when the name is not legible Signatures (§7.3.10)
Logo MUST be [logo: printed words], or bare [logo] when it prints no text Logos (§12.1.3)
Watermark MUST be [watermark: printed words], first in its page's content Watermarks (§7.3.13)
Stamp MUST be [stamp: printed words], or bare [stamp] when illegible Stamps (§7.3.11)
A printed character that is also Markdown syntax MUST be escaped — \*\*, \_, \|, \` — and MUST NOT be dropped to avoid the collision Escaping Printed Marks (§7.2.4)

Reading the examples. Each one pairs a source page with the output the rule expects. ✅ Sample: the rule applies. ❌ Counter-sample: it looks like it applies and does not, or a rendering got it wrong. A non-conforming output, in red, is shown only for contrast. … marks content left out of an excerpt.

The point, in a small example

Compare visible glyph styles, background highlighting, raised/lowered text and mathematical notation. Each has its own encoding. These pages are made up to isolate the rule.

01

✅ SampleConstructedThe rule applies

Preserve bold and italic without inventing emphasis

Only “Urgent” is bold and only “review” is italic. The rest stays plain.

Source page
Text Formatting Conventions — Preserve bold and italic without inventing emphasis. Source page.
Non-conforming output

What the rule rules out.

Markdown
**Urgent review required.**
Expected output
Markdown
**Urgent** *review* required.
Text Formatting Conventions · Source page

Preserve bold and italic without inventing emphasis

Text Formatting Conventions — Preserve bold and italic without inventing emphasis. Source page.
02

✅ SampleConstructedThe rule applies

A yellow highlight has its own markup

Preserve the yellow background as a highlight; it does not imply bold or meaningful yellow text.

Source page
Text Formatting Conventions — A yellow highlight has its own markup. Source page.
Non-conforming output

What the rule rules out.

Markdown
Bring **photo ID** tomorrow.
Expected output
Markdown
Bring <mark style="background-color: yellow">photo ID</mark> tomorrow.
Text Formatting Conventions · Source page

A yellow highlight has its own markup

Text Formatting Conventions — A yellow highlight has its own markup. Source page.
03

✅ SampleConstructedThe rule applies

Underline is not italic

The entire printed sentence is underlined. Use the underline tag, not Markdown underscores.

Source page
Text Formatting Conventions — Underline is not italic. Source page.
Non-conforming output

What the rule rules out.

Markdown
_Return by Friday._
Expected output
Markdown
<u>Return by Friday.</u>
Text Formatting Conventions · Source page

Underline is not italic

Text Formatting Conventions — Underline is not italic. Source page.
04

✅ SampleConstructedThe rule applies

Raised references and lowered chemical indices

These are non-mathematical raised and lowered characters. Keep them as tags, not Unicode substitutions.

Source page
Text Formatting Conventions — Raised references and lowered chemical indices. Source page.
Non-conforming output

What the rule rules out.

Markdown
Water: H₂O

See note³
Expected output
Markdown
Water: H<sub>2</sub>O

See note<sup>3</sup>
Text Formatting Conventions · Source page

Raised references and lowered chemical indices

Text Formatting Conventions — Raised references and lowered chemical indices. Source page.
05

✅ SampleConstructedThe rule applies

An equation inside a sentence

This is mathematical notation, so encode the equation as LaTeX with double-dollar delimiters, even inside a sentence.

Source page
Text Formatting Conventions — An equation inside a sentence. Source page.
Non-conforming output

What the rule rules out.

Markdown
The energy is $E = mc^2$.
Expected output
Markdown
The energy is $$E = mc^{2}$$.
Text Formatting Conventions · Source page

An equation inside a sentence

Text Formatting Conventions — An equation inside a sentence. Source page.

Why HTML elements at all

Markdown has no syntax for underline, superscript, subscript or highlight. The HTML element passes through every downstream Markdown renderer unchanged, and it survives a round-trip: a reader can strip it, render it or read the base characters underneath. A Unicode substitute (², ₂) does not, which is why Superscript and Subscript (§7.2.11) forbids it.

  • Markdown Rendering§3.2the block-level constructs, of which this table is the inline half
  • Elements§3.1the Text class takes its inline marks from this table
  • Quick Reference§D.1every rule's requirement on one page

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Rule id text-text-formatting-conventions · text formatting inline