Different behaviour on extension of a Base function after searching it in REPL about julia HOT 3 CLOSED

Perhaps better example:

julia> module A
         setproperty!(x) = x
       end
Main.A

julia> A.setproperty! == setproperty!
false

julia> module B
         const c = setproperty!  # just use it
         setproperty!(x) = x
       end
ERROR: invalid method definition in B: function Base.setproperty! must be explicitly imported to be extended
Stacktrace:
 [1] top-level scope
   @ none:0
 [2] top-level scope
   @ REPL[3]:3

from julia.

This is intentional and an explicit feature of the languag. Base functions can be shadowed, if they haven't been referred to before.
One major advantage of this is that it allows Base to export new symbols without breaking existing code, while also preventing Base from monopolizing a huge number of names.

from julia.

indeed this is a great feature...my case was specifically referred to the help search side effect which can be a bit surprising, but, at the same time, it makes sense because if you search for a name, it is much more likely that you want to extend it than if you don't do so. So, I guess it is a good default

from julia.