Am So., 16. Aug. 2020 um 14:32 Uhr schrieb Shiro Kawai <xxxxxx@gmail.com>:
>
> A port can be accessed from multiple threads, so it might be better to make port flags either port-and-thread-specific, or having (with-port-flag thunk) that locks the port.

Thread-specific port flags would be wrong (this is also not true for
the implicit "fold-case" flag of R7RS). If one thread switches the
mode and writes some directive to a given port, the writer of the
other thread needs to know that this directive is active on that port.
Otherwise, the resulting data may be garbage.