The substitution of a variable value from an object is very similar to normal variable substitution. However, instead
of using the dollar sign ($) to substitute a value, you use the at sign
(@). Syntactically, the only difference between referencing a variable value with
@ instead of $ is that dots
(.) and square brackets ([]) are allowed as part of the
object name.
A literal at sign (@) can be placed inside of an attribute's value by typing the
character twice consecutively (e.g., <setvar email="jlx@@commandprompt.com" />).
