[Proposal]: Add a way to inherit documentation <inheritdoc />

[DustinCampbell]

• Discussion: Add a way to inherit documentation <inheritdoc /> #8984

Summary

(moved from part of dotnet/roslyn#67 by @dfkeenan, with part of the request tracked at #315)

Hi,

Please add <inheritdoc /> tag or similar:

I think it would be really handy if the compiler(s) when outputting the documentation XML file if it could use inherited documentation where available/requested. Though I am not sure what should be output if there is no documentation available.

P.S. A Diagnostic and Code Fix that generates document comments for me would also great 😃