Where is `isa` defined

Internals & Design
1 
julia> @less 1 isa Int
ERROR: could not determine location of method definition

How else can I locate the method definition? Grepping for isa is tricky.

2 

julia> methods(isa)
# 1 method for builtin function "isa":
[1] isa(...) in Core
3

Built-in functions print (built-in function) if you evaluate them (just their name) in the REPL:

julia> isa
isa (built-in function)

julia> getfield
getfield (built-in function)
4

Aye, but where is this built-in function defined?

5

Bermuda triangle.

julia> methods(isa)[1].file
Symbol("")

julia> methods(isa)[1].line
0
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