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Description
The only reason to use scoped-based namespace declarations is when there is more than one namespace define in a file. Since this condition should be avoided in production code, I propose the guideline: Do use file-based namespace declarations.
This wording, however, may not be clear enough. Perhaps Do use file-based namespace declarations and avoid scope-based namespace declarations.
I suspect that over time scope-based namespace declarations will disappear except in legacy code.