VO-DML 1.1 progress

The proposed modifications to the standard are being managed by issues connected to the github repository. It is best to conduct discussions there.

In particular the 1.1 milestone collects the issues that are expected to be complete for 1.1 and the issues tagged "VO-DML Language" are those that specifically relate to the VO-DML standard rather than the wider topic of the VO-DML tooling (which is in the same repository).

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