MathMLForm, live
Any output cell reaches this through its form selector; out-form pins it.
source
<notatio-cell value="Sqrt(x ^ 2 + y ^ 2)" out-form="mathml" box />MathML
A text output form: presentation MathML, surfaced as the MathMLForm form. It is a pure function of the MathJSON tree — no engine, no canonicalisation — so the same tree always prints the same string, with attributes in a fixed order.
Unlike Wolfram FullForm, MathML does not round-trip. The registry format MathML (aliases mathml, MathMLForm) has an encode and no decode (packages/formats/src/formats.ts), because there is no MathML parser on the other side. That is a freedom rather than a limitation: the emitter owes nothing to being read back, so it can pick whatever typesets best — a <mfrac> for a Divide, an <msqrt> for a Sqrt, a zero-thickness <mfrac> in delimiters for a Binomial.
Parenthesisation is precedence-driven the way a TraditionalForm printer works: every node reports how tightly it binds, and a parent wraps a child in <mo>(</mo> … <mo>)</mo> only when the child binds looser than the slot it is going into.
| Registry name | MathML |
| Aliases | mathml, MathMLForm |
| MIME types | application/mathml-presentation+xml, application/mathml+xml |
| Extension | .mml |
| Direction | export only |
:mime application/mathml+xml in the CLI resolves to it, and :formats shows it with [export] and no import.
There is no in-form="mathml" counterpart — with no decoder, there is nothing to type into.
Each row below shows an expression and its presentation MathML.