even if there is one on upper node

This is a particular logic allowed by paragraph 7.3.3 Identifier
of OGC 18-010r6

This is a particular logic allowed by paragraph 7.3.3 Identifier
of OGC 18-010r6

This is the standard logic, that is now possible since ID is
allowed in BASEGEOGCRS and similar node

- Allow ID[] in base CRS of Derived CRS
- Allow VERSION[] in non-conversion coordinate operations
- Use VERSION[] to set operationVersion member of CoordinateOperation
- Export operationVersion in WKT2:2018

Breathe 4.12.0 (as pulled by MacOSX builds such as
https://travis-ci.com/OSGeo/proj.4/jobs/185395222)
does not seem to like default initialization in documented C++ structs (regression/bug)

/Users/travis/build/OSGeo/proj.4/docs/source/development/reference/cpp/io.rst:6:Parsing of expression failed. Using fallback parser. Error was:
Error in postfix expression, expected primary expression or type.
If primary expression:
  Invalid definition: Expected identifier in nested name. [error at 67]
    std::string osgeo::proj::io::AuthorityFactory::CRSInfo::authName = {}
    -------------------------------------------------------------------^
If type:
  Invalid definition: Expected identifier in nested name. [error at 67]
    std::string osgeo::proj::io::AuthorityFactory::CRSInfo::authName = {}
    -------------------------------------------------------------------^

And publish link to corresponding promoted and public OGC doc:
http://docs.opengeospatial.org/as/18-005r4/18-005r4.html