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This xsi:type is defined by the urn:mace:shibboleth:2.0:resolver schema 3.3, which is located at http://shibboleth.net/schema/idp/shibboleth-attribute-resolver.xsd.
Prior to V3.3 supplied plugins were defined by a schema type ( xsi:type ) in the urn:mace:shibboleth:2.0:resolver:dc schema, which is located at http://shibboleth.net/schema/idp/shibboleth-attribute-resolver-dc.xsd. This is still supported, but every element or type in the urn:mace:shibboleth:2.0:resolver:dc schema has an equivalently named (but not necessarily identical) version in the urn:mace:shibboleth:2.0:resolver schema. The use of the urn:mace:shibboleth:2.0:resolver schema also allows a relaxation of the ordering requirements of sub elements and so a more natural order can be applied. Note that versions earlier than 3.3 are no longer supported and you should look to upgrade at the soonest opportunity.
When specified in the urn:mace:shibboleth:2.0:resolver namespace the name was dc:Script
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