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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:encoder schema , which is located at http://shibboleth.net/schema/idp/shibboleth-attribute-encoder.xsd. This is still supported, but every element or type in the urn:mace:shibboleth:2.0:encoder schema has an identically named version in the urn:mace:shibboleth:2.0:resolver schema.
Attributes
Any of the common attributes can be specified. In addition, the following are supported:
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