Actually, from man perlop:

qr/STRING/imosx
   This operator quotes (and possibly compiles) its
   STRING as a regular expression.  STRING is inter­
   polated the same way as PATTERN in "m/PATTERN/".
   If "'" is used as the delimiter, no interpolation
   is done.  Returns a Perl value which may be used
   instead of the corresponding "/STRING/imosx"
   expression.

A little experiment:

use strict
my %a = (qr/(.+)pippo/, 1);
print keys %a;
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prints out (?-xism:(.+)pippo), which can be used in the matching part of a regex, while

use strict;
my %a = (1,2);
my %b = (\%a, 3);
for (keys %b) { print %$_ };
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dies with error
Can't use string ("HASH(0x81005ac)") as a HASH ref while "strict refs" in use at - line 5.

The stupider the astronaut, the easier it is to win the trip to Vega - A. Tucket