The "context" property currently has a fixed string enumeration values. This should not be fixed by the schema, but an externally defined code list should be used instead. Not all issuers have the same set of these values in use.
The type of the "audience" properly should also be changed into gml:CodeType for this reason.
"alertnessLevel" of WarningTextSectionType should be changed into a more generic "severity". It should also be changed into a code from enumeration.