Using defs declared in different files

I had this basic doubt about whether we can somehow <use> the <defs>
declared in some other file..... Like we do the same in C++ where we declare
the whole class in a different header file and make use of it and provide
its definitions in another file. Even in javascript we are allowed to do
that like say provide a whole library of functions in a javascript file...
Declare that file at the top of this javascript file and then use the
functions from there....
Similiarly is it possible to use such cases with only SVG! defs and use?
Isnt this a useful feature for UI widgets using SVG!

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Regards,
Ganaraj P R