mml:* — Any element from the MathML namespace
mml:* ::=
*:*
This position in a content model can be occupied by any element in the MathML namespace.
The Mathematical Markup Language Recommendation from the W3C defines the Mathematical Markup Language, or MathML. MathML is an XML application for describing mathematical notation and capturing both its structure and content.
A complete description of MathML is outside the scope of this reference.