IsNotMatching('no loop linebreak', 'a\R\Rb', 'a'#13#10'b');
  IsNotMatching('   loop linebreak', 'a\R+\Rb', 'a'#13#10'b');

• The first test works, \R eats the entire #13#10. The 2nd #R does not match.
• Yet the 2nd test (which also must match 2 linebreaks does match.

In a OP_STAR (FindRepeated) OP_ANYLINEBREAK changes its preference to match #13#10 as 2 breaks rather than 1. So the same pattern has different behaviour.