Documenting types after definition

[alhirzel]

The documentation section "Types" within "Documentation" does not mention that the following is possible for an already-existing type T4:

"..."
T4

The linked documentation is consistent with #15623, which implies that this syntax should not work. On Julia 1.1.0, however, the above syntax appears to work in the REPL. Additionally, there exist guidelines which separate documentation from code, and this "remote documentation" of a type is needed to meet these guidelines.