See documentation for the Mathematical Markup Language (MathML) 2.0 DTD.
The alttext is used only within mathematical expressions. The equivalent function, providing words that can be display “behind” a graphic or be pronounced over a graphic, is performed by the <alt-text> element for graphics (and other elements) within the NCBI Book DTD (or NCBI Collection DTD).
| Value | Meaning |
|---|---|
| Data characters | See MathML documentation. |
| Restriction: This attribute may be specified if the element is used. | |