Matterhorn 17-002 · PDF/UA-1 UA1:7.7-1

Formula tag with no Alt: writing maths a listener can follow

A Formula element has no /Alt giving the expression in words.

What a screen reader actually does

The reader announces "formula" and stops.

What is in the file

A Formula is a structure element like any other. The spoken form is its /Alt entry:

31 0 obj
<< /Type /StructElem
   /S /Formula
   /P 12 0 R
   /Pg 4 0 R
   /Alt (x equals, fraction, negative b plus or minus the square root of b squared minus 4 a c, over 2 a, end fraction.)
   /K [ 9 ]
>>
endobj

Condition 17-002 is a Formula with no /Alt. Taggart also reports an /Alt that is empty or only spaces, since it gives the listener the same nothing.

What the reader hears

The Formula role, and nothing to go with it. Taggart’s own screen-reader preview puts it this way for such an element:

formula — no description available; the reader announces the role and nothing else

Some readers may fall back to the characters inside instead, which gives the glyph-by-glyph reading described under 17-001: symbols in drawing order, superscripts flattened, fraction bars silent. Neither is the expression.

Writing the description

Write what you would say reading the expression aloud to someone taking notes, so that they could write it down again correctly.

Say where groups begin and end. Sighted readers get grouping from layout; a listener gets it only from words. The square root of b squared minus 4ac is ambiguous; the square root of, b squared minus 4 a c, end root is not. Fraction … over … end fraction does the same for division.

Use words, not symbols. Less than or equal to, not ≤. Speech engines name symbols differently, and some skip the ones they do not know.

Name it if it has a name. The quadratic formula: x equals… tells the listener what is coming before they have to hold it in their head.

Do not describe the typesetting. A large fraction with a radical in the numerator is a picture of the formula, not the formula.

One Formula per displayed line in a multi-line derivation, each with its own /Alt, so a listener can move through them one step at a time.

If the expression is in a different language from the text around it, give the Formula its own /Lang.

How to add it free, in Acrobat Pro

From Adobe’s Tags panel documentation — it describes these steps for figures and links, and the same Properties dialog serves every tag (Adobe: Edit document structure with the Content and Tags panels):

1. Open the Tags panel: View → Show/Hide → Side Panels → Tags (the hamburger menu on Windows).
2. Find the <Formula>. Selecting the expression on the page and choosing Find Tag From Selection from the panel’s Options menu jumps to it; Highlight Content confirms you have the right one.
3. Choose Properties from the Options menu.
4. On the Tag tab, type the description into Alternate Text and close the dialog.

Two Acrobat features that look as if they would help do not. The Add alternate text action under Prepare for accessibility steps through figures — Adobe describes it as detecting all figures — so it does not visit formulas. And the Accessibility Checker’s Other elements alternate text rule, as Adobe describes it, covers things like multimedia, annotations and 3D models, not formulas. (Adobe: Create and verify PDF accessibility)

At the source. Microsoft says Word, and PowerPoint for Windows from version 2602, now write MathML into the exported PDF for native Office Math. Whether a given export also writes /Alt is worth checking in the Tags panel rather than assuming — this condition only looks at /Alt. For LaTeX, see LaTeX to accessible PDF.

What Taggart does

Taggart reports every Formula whose /Alt is missing, empty or blank, as a blocker, with its page and structure path:

<Formula> has no /Alt attribute giving the expression in words.

/ActualText alone does not satisfy it. That is stricter than veraPDF, whose rule 7.7-1 accepts either entry, and it follows the protocol’s wording. (veraPDF PDF/UA-1 rules)

The repair, formula-alt-text, is not one of the safe fixes. In the application each formula without a description goes to the review queue, with a field for the words. Where the document itself holds text that might describe it — a caption, a line beside it — the queue lists that too, each piece labelled with where it came from. The repair writes exactly what you approve for each formula, by its structure path, and nothing else. Asked to run with no description supplied, it refuses:

formula alt text must be supplied by a human

Taggart does not generate formula descriptions. A spoken form of an expression is a translation, and a fluent wrong one — x squared for x sub 2 — is worse than none, because nobody listening can tell.

How Taggart handles it

Taggart checks for this condition automatically and reports it as a blocker, with where in the file it found it.

The fix is Add alternative text to formulas. It changes what the document means, so Taggart proposes it and waits for your approval rather than applying it unattended.

Where this sits in the standards

Related conditions

• 17-001 Content is a mathematical expression but is not tagged with a Formula tagAn equation is tagged as a paragraph or a figure rather than a Formula.
• 17-003 Unicode mapping requirements are not met for a formulaMathematical glyphs — often from a symbol font with no ToUnicode — cannot be mapped to Unicode.
• 13-004 Figure tag alternative or replacement text missingA Figure element has neither /Alt nor /ActualText. Every Figure must have one or the other; if the image is decorative it should be an artifact instead of a Figure.
• 13-005 ActualText used for a Figure for which alternative text is more appropriateActualText replaces the content for text-extraction purposes; Alt describes it. A photograph needs Alt. A drop cap or a glyph-as-image needs ActualText.

Other conditions in checkpoint 17

Checkpoint 17 covers mathematical expressions. These are its other failure conditions; the ones without a link are in the rule set but do not have a written page yet.

• 17-001 Content is a mathematical expression but is not tagged with a Formula tagAn equation is tagged as a paragraph or a figure rather than a Formula.
• 17-003 Unicode mapping requirements are not met for a formulaMathematical glyphs — often from a symbol font with no ToUnicode — cannot be mapped to Unicode.

Checked with Taggart on a generated file that fails this condition on 2026-10-02. The Acrobat steps follow Adobe’s documentation and were not walked through by hand. Last updated 2026-10-02.