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With SAML 1.1, there was a completely undefined concept called an AttributeNamespace used as a secondary naming key. In Shibboleth, we defined a fixed value to use, urn:mace:shibboleth:1.0:attributeNamespace:uri, that is automatically matched. If you actually need to support SAML 1.1 in 2018now, you probably have bigger problems than how to use the SP, but chances are you might run into some made up value, and you'll need to include that value in the rule as the nameFormat.
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