Binary dollar sign operator

Hi everyone,
I was reading an XML file describing a style for highlighting Julia syntax, when I noticed in the “operators” category the operators $ and $=. I only know $ for string interpolation, and that’s the only result I find for $ if I search online. That’s also the only result the REPL returns if I search $ in help mode:

help?> $

  $

  Interpolation operator for interpolating into e.g. strings and expressions.

Interestingly, for $= I get

help?> $=
search: >= = $ .= <= != ==

  x $= y is a synonym for x = x $ y

but what is this binary $ operator exactly? I can’t find it in the documentation…

I think the docstring is just indicating that the $= is syntactically available, even though it’s not yet defined as a function. For example:

julia> ($)(x, y) = (x, y);

julia> x = 1;

julia> x $= 2
(1, 2)
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