saint-

grammar G {
    token TOP { <sentRefEnd> }
    token sentFrag { <char>+? <?before <endPunc>> }
    token sentRefEnd { <sentFrag> <endPunc> <ref> }
    # token sentRefEnd { <char>+? <endPunc> <ref> }
    token endPunc { \. }
    token char { \w || \s }
    token ref { \(\d+\) }
}

my $book = "Hello.(1)";
my $match = G.parse($book);
say $match;