Msc-generator supports an extended version of the DOT language, which is fully backwards compatible with the original saving two exceptions.
defstyle,
defproc, replay, defdesign, usedesign, include,
cluster, if, then and else. If you want these as nodes
put them in-between quotation marks.
The language of the graphs (the DOT language) is documented well on the graphviz pages at http://www.graphviz.org/. Below we just list the additions by Msc-generator.