Role of <mstack>
Builds stacked arithmetic and related layouts. Use the element for its semantic role rather than as a visual styling shortcut. Assistive technology, browser math layout, conversion tools, and copy-and-paste behavior all depend on the markup preserving the mathematical structure.
Example markup
<mstack><mn>12</mn><msrow><mo>+</mo><mn>3</mn></msrow></mstack>Allowed children
stack rows and line elements
Only place children inside <mstack> when they match the element's content model. Validate the complete MathML tree after conversion because a locally valid fragment can still be incorrect in its parent context.
Implementation notes
- Support is less universal than core Presentation MathML.
Accessibility and testing
- Keep a meaningful DOM structure instead of replacing the expression with an image.
- Test keyboard selection, screen-reader output, browser rendering, and conversion back to LaTeX.
- Check that fallbacks do not expose raw tags or omit the mathematical relationship represented by <mstack>.