Cannot get REPL help for .= operator

[eschnett]

The REPL help mode (entered by pressing ?) cannot handle the .= operator:

help?> .=
ERROR: LoadError: Invalid @var syntax `invalid identifier name ".="`.
Stacktrace:
 [1] error(::String) at ./error.jl:33
 [2] splitexpr(::Any) at ./docs/bindings.jl:28
 [3] bindingexpr(::Any) at ./docs/bindings.jl:17
 [4] lookup_doc(::Expr) at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/REPL/src/docview.jl:137
 [5] docm(::LineNumberNode, ::Module, ::Any) at ./docs/Docs.jl:501
 [6] @doc(::LineNumberNode, ::Module, ::Expr, ::Vararg{Expr,N} where N) at ./boot.jl:451
in expression starting at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/REPL/src/docview.jl:301

[fredrikekre]

#29282, #29361, #26933, #24871, #22013