Empty semantics (invalid): $$

annotation (invalid): $annotation$

annotation-xml (invalid): $\text{annotation-xml}$

presentation MathML (no annotations): $\text{presentation MathML}$

content MathML (no annotations): $\mathrm{content\; MathML}$

presentation MathML ; annotation: $\text{presentation MathML}$

presentation MathML ; annotation-xml: $\text{presentation MathML}$

content MathML ; annotation: $\mathrm{content\; MathML}$

content MathML ; annotation-xml: $\mathrm{content\; MathML}$