OpenMath encodes the semantics, i.e. the meaning of mathematical formulas. It uses so called content dictionaries which define the meanings of symbols used in the formula. These content dictionaries are referenced by URI. This makes OpenMath extensible. Every formula can be encoded, even if it uses symbols of a new theory. OpenMath can not encode how a formula is presented to the user. If you need that, take a look at MathML.