= MathML Core
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\b[MathML Core] is a browser-oriented subset of <MathML> with specified rules for mathematical presentation and layout. The pinned 24 June 2025 document is a Candidate Recommendation Snapshot. It defines a concrete target for implementation, rather than identifying the whole <MathML> language with one browser's output.<MathML Core by World Wide Web Consortium>[Abstract; Status of This Document; §2.1 elements and attributes]{ref}
For an original example, encode a <typeset fraction> surrounded by parentheses as `<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mo stretchy="true">(</mo><mfrac><mi>x</mi><mn>2</mn></mfrac><mo stretchy="true">)</mo></mrow></math>`. The row has three children: a left <mathematical delimiter>, the <typeset fraction> and a right <mathematical delimiter>. The fraction's children supply <numerator> $x$ and <denominator> 2.
The parentheses are <stretchy mathematical operators>: their markup requests size-sensitive layout around the fraction. Core specifies operator stretching and row layout; <mathematical glyph variants> or <mathematical glyph assemblies> can supply suitable forms.<MathML Core by World Wide Web Consortium>[§§3.2.4.3, 3.3.1.1 and3.3.2: operator layout, stretching and fractions]{ref} This illustrates why presenting a formula requires more than placing all its characters on one <text baseline>.
Changing `stretchy="true"` to `stretchy="false"` changes the layout instruction without changing the fraction's two operands. Exact dimensions also depend on the <computer font> and applicable layout properties. The markup supplies structure and presentation instructions; substituting a numerical value for $x$ and evaluating the quotient is a separate operation.
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