STC Notes update

[Arnold Rots]

Just FYI:

The two STC-related Notes, STC-S and STC-Model, have been updated.

    http://www.ivoa.net/Documents/latest/STC-S.html
    http://www.ivoa.net/Documents/latest/STC-Model.html

The schema was updated November 26: improved consistency between
abstract and nillable attributes of elements, mainly involving head
elements of substitution groups; this expands the elements that can be
used in references and is fully downward compatible.
The STC-Model Note now includes a table of all global elements with
their abstract, nillable, and referencing properties, as well as
substition group membership.

  - Arnold

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Arnold H. Rots                                Chandra X-ray Science Center
Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
60 Garden Street, MS 67                              fax:  +1 617 495 7356
Cambridge, MA 02138                             arots at head.cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
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