We present semantic markup as a way to exploit the semantics of mathematics in a wiki. Semantic markup makes mathematical
knowledge machine-processable and thus allows for a multitude of useful
applications. But as it is hard to read and write for humans, an editor needs to understand its inherent semantics and allow for a human-readable presentation. The semantic wiki SWiM offers this support for
the OpenMath markup language. Using OpenMath as an example, we
present a way of integrating a semantic markup language into a semantic
wiki using a document ontology and extracting RDF triples from XML
markup. As a benefit gained from making semantics explicit, we show
how SWiM supports the collaborative editing of definitions of mathematical symbols and their visual appearance.