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§7.2.11

Superscript and Subscript

A superscript—a tag or a Unicode glyph?

✅ NormativeSettled. The requirement holds as written.📄 Page ruleCan be applied from the page alone.Read §7.2.11 in the RFC ↗

The requirement

Raised and lowered text outside maths MUST be written with <sup> and <sub>. A Unicode superscript or subscript character MUST NOT be substituted for the tag.

When it applies

Sketch of the printed page — layout, not output
H<sub>2</sub>O        ← conforming
H₂O                   ← non-conforming

The same applies to superscripts: x<sup>2</sup>, not x². Inside an equation, raised and lowered terms are LaTeX ^{…} and _{…} within $$ … $$ — see Inline Equations (§7.2.6).

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

Raised text can be a reference marker or part of an equation. The two cases use different representations. These pages are made up to isolate the rule.

01

✅ SampleConstructedThe rule applies

A footnote marker and a mathematical exponent differ

The first raised 2 is a note reference and uses <sup>. The second belongs to a mathematical expression and stays inside LaTeX. Do not turn both into Unicode ² or apply one markup to both.

Source page
Superscript and Subscript — A footnote marker and a mathematical exponent differ. Source page.
Expected output
Markdown
See note<sup>2</sup>

Then compute $$x^{2}$$.
Superscript and Subscript · Source page

A footnote marker and a mathematical exponent differ

Superscript and Subscript — A footnote marker and a mathematical exponent differ. Source page.
02

✅ 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
Superscript and Subscript — 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>
Superscript and Subscript · Source page

Raised references and lowered chemical indices

Superscript and Subscript — Raised references and lowered chemical indices. Source page.

Why the tag

A tag round-trips: a reader can strip it, render it, or read the base character underneath. A Unicode glyph is lossy in the other direction — ₂ does not compare equal to 2, so a downstream numeric parse or string match silently fails. Unicode also has no raised or lowered form for most characters, so substitution cannot be applied consistently.

Inside table cells

A footnote superscript attached to a value — 48,210³ — MUST be tagged as 48,210<sup>3</sup>. Whether the marker stays in the cell is a separate question, answered by Marks and Symbols in Cells (§9.6.6).

A raised marker that is itself Markdown punctuation is tagged and escaped: <sup>\*\*</sup> — see Escaping Printed Marks (§7.2.4).

More

Rule id text-superscript-and-subscript · text formatting inline