In practice, application software which understands if and where qnames have been used in content and security software responsible for performing Canonicalization are distinct layered components.
In principle it would be possible to define APIs to allow applications to specify prefixes to include in the Prefix List. For example, Canonicalization and hence a Prefix List may be associated with each element.
An example would be when a SAML assertion is signed and then carried somewhere in a SOAP message.
However, in the environment described above, problems can arise even when using Exclusive Canonicalization.
When the namespace defines some critical aspect of the semantics of a qname with this tag, this will create ambiguity even though the XML is digitally signed.