That's a very good point!

But it's not the interpolation, but more generally the stringification .

 
use v5.12;
use warnings;

$a= 1-1e-16;

printf "%.16f\n",$a;
printf "%.16f\n",("".$a);
[download]

0.9999999999999999
1.0000000000000000
[download]

Consequently this should be documented for stringification, and print should reference it.

Update

Apart from mentions in perlglossary and overload there is not much on stringification to be found in perldocs :/

https://perldoc.perl.org/perlglossary#stringification