Empty semantics (invalid):

annotation (invalid): annotation

annotation-xml (invalid): annotation-xml

presentation MathML (no annotations): presentation MathML

content MathML (no annotations): content MathML

presentation MathML ; annotation: presentation MathMLannotation

presentation MathML ; annotation-xml: presentation MathMLannotation-xml

content MathML ; annotation: content MathMLannotation

content MathML ; annotation-xml: content MathMLannotation-xml