Parsing the \special command including the DVIview_diagram or
drawfile commands is done in the procedure ParseDiagram which is called
from DoSpecial, both in the file dvimisc.c. The reason for not using the
existing DoSpecial is that the format of these \special commands differs
quite a bit from the one assumed for the other \special commands supported.
ParseDiagram will read all the parameters, call diagram with these and return
_TRUE if the \special command was related to diagram printing,
_FALSE otherwise.
Reading the arguments I allow somewhat more variations than DVIview does. Usually
everything can be separated by ",", "=" or " ".