MathML captures the presentation of a mathematical formula
(Presentation MathML) or the meaning of a formula (Content
MathML). Concerning the presentation of a formula, MathML is quite
advanced. About Content MathML it has to be said that it
is not suited to store the meaning of
every formula. The specification says about that:
The
base set of content elements is chosen to be adequate for
simple coding of most of the formulas used from kindergarten to
the end of high school in the United States, and probably beyond
through the first two years of college, that is up to A-Level or
Baccalaureate level in Europe.
MathML has some functionality
for extensions, but if you need more than MathML provides, you are
probably better off with
OpenMath.