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defnval Expressions
The defnval expression allows access to the value of a let variable in an expression sequence. The expr attribute of a <defnval> element must be equal to the name of a let variable defined under the mapping rule’s <define> element.
The following feature mapping rule shows how to access the value of a let variable in an expression sequence:
<mapping match="..."> ... <define> <let name="theFeatureType"> <!-- some expression sequence --> </let> </define> ... <feature-type> <defnval expr="theFeatureType"/> <feature-type> ... </mapping>