f'{42!r}'
f'{42!s}'
f'{42!a}'
f'{42<error descr="An illegal conversion character 'z': should be one of 's', 'r', 'a'">!z</error>}'
f'{42<error descr="An illegal conversion character 'foo': should be one of 's', 'r', 'a'">!foo</error>}'
f'{42<error descr="A conversion character is expected: should be one of 's', 'r', 'a'">!</error>}'
f'{42<error descr="A conversion character is expected: should be one of 's', 'r', 'a'">!</error>:2}'