Non-capturing parens ((?:...)) are just like parens ((...)) in Perl code. The alter precedence.

# Matches strings that include "ab" or "cd"
/ab|cd/

# Matches strings that include "abd" or "acd".
/a(?:b|c)d/
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(?=...) performs a match, but leaves pos unchanged after the match.

local $_ = 'foo bar bar baz';
my $term = 'bar';

my $num_matches = () = /(?:\W|^)\Q$term\E(?:\W|\z)/g;
print("$num_matches\n");
# 1: foo[ bar ]bar baz

my $num_matches = () = /(?:\W|^)\Q$term\E(?:(?=\W)|\z)/g;
print("$num_matches\n");
# 2: foo[ bar][ bar] baz
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