"show" nested struct

General Usage
3

This does call show(io, A), but note that print calls the two-argument show function. You typically define the 3-argument show in addition to the 2-argument show, if you want a more verbose multi-line pretty-printing in addition to compact output (for use in e.g. REPL output via display), as explained in the manual on Custom pretty printing.

I’m not sure what you mean — you can still add indentation metadata to IOContext in the same way:

Base.show(io::IO, ::MIME"text/plain", a::A) = print(io, ' '^get(io, :indent, 0), ">>A$(a.x)")
function Base.show(io::IO, mime::MIME"text/plain", b::B)
    indent = get(io, :indent, 0)
    println(io, ' '^indent, "B containing:")
    show(IOContext(io, :indent => indent+4), mime, b.x)
end

which gives

julia> B(A(1))
B containing:
    >>A1
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