this is a matter of opinion. personally i think SymbolGraphGen would be better off emitting all the symbols by default (regardless of implicitly private access), but others feel strongly that underscored APIs are not public APIs and therefore should not be picked up by documentation compilers.
this is not a DocC issue, as DocC is a consumer of SymbolGraphGen, just like swift-biome is.
related discussion: (SymbolGraphGen) can we make `isImplicitlyPrivate` checking configurable?
cc @franklin