Mumps variables

Kevin OKane in his Mumps tutorial/book states:

"A Mumps variable name must begin with a letter (A through Z) or percent
sign (%) and may be followed by either letters, the percent sign, or
numbers."

However, in some of the examples that follow, e.g.:

set ^a="test" write ^a,!

The variable name starts with a "^". The example worked correctly with
Ray Newman's Mumps. I just need clarification as to exactly how a Mumps
var should be named. TIA...
-- 
Duke Normandin