A union color set is a disjoint union of previously declared color sets.
colset name = union id1[:name1] + id2[:name2] + … + idn[:namen];
namei is omitted then
idi is treated as a new value, and it can be referred to simply as
first after selectors, then after ordering of each base color set
v has type
colset Data = string with “A”..”z” and 0..8;
colset Packet = union DATA:Data + ACK;
var packet : Packet;
The CPN variable
packet may have values of the form
DATA str where
str is a string containing only letters and has length up to 8. For example,
DATA "contents' are legal values, but
DATA are not.
See also color set functions.