VOID expressions return no value but are used to
perform other work. The
VOID UNIQUE expression deletes every value of a property
except the first.
The name of the property is given in a
PROP_NAME expression node. For example, if the “Color”
property has three values, “red”, “blue”, and “green”, then the
UNIQUE expression removes the values “blue” and
“green”, leaving just the value “red”.
See the
EXPRESSION element for DTD and attribute information.
