An undefined name was encountered. This could be a variable name, an element name, an attribute name, or a type name. It may be that you misspelled the name or referred to it in the wrong namespace.

If it is a variable name, that variable may be referenced outside the scope for which it is bound. One reason for this error is misplaced or missing parentheses. A common case is when you attempt to return two items using a FLWOR expression, as in:

for $prod in doc("catalog.xml")//product
return $prod/number, $prod/name

In this case, the second reference to $prod on the last line is out of scope, because only a single expression is included in the return clause. The rest of the line (, $prod/name) is considered to be a separate expression that appears after the FLWOR expression. This example can be remedied by placing parentheses around the return clause, as in:

for $prod in doc("catalog.xml")//product
return ($prod/number, $prod/name)

If an element, attribute, or type name raises the error, it appears in a sequence type but is not part of the in-scope schema definitions. For example, the sequence type:

schema-element(prod, ProductType)

will raise an error if the in-scope schema definitions do not include a declaration for a prod element and a type definition for ProductType.