The validSubLocales attribute is defined on many elements.
We only use validSubLocales currently in collation/, but they don't add any value. Any implementation can simply get them from the sublocales in main/. So they are really only a possible source of errors, and we are better off removing them.
The cp element was a hack that we had to represent values that XML doesn't permit, like control codes. However, we always use a hex notation (like \uxxxx) for those now, and don't need it.
We should also deprecate references in ldml elements, since we don't use those.
FYI: The following elements are not found in the data, but are not deprecated. They should be reviewed as well.
Unused (but not deprecated) attributes are found in column F of
The distinguishing attributes are marked with *.
«NONE» means that the element is found with no attributes sometimes.