f'{42}'
f'{42!r}'
f'{42!r:03}'
f'{42:03}'
f'{42!r:{y}.{z}}'
f'{<error descr="expression expected"><error descr="} expected">'</error></error>
f'{42:{<error descr="expression expected"><error descr="} expected">'</error></error>
f'{42!r:{<error descr="expression expected"><error descr="} expected">'</error></error>
f'{{'
f'{{{<error descr="expression expected"><error descr="} expected">'</error></error>