Date/Time parsing of ISO 8601 timestamps with commas

I noticed today that PostgreSQL doesn't support parsing ISO 8601 timestamps
that use a comma as the decimal separator.

The section of the standard that describes this is 4.2.2.4

> the decimal fraction shall be divided from the integer part by the decimal
> sign specified in ISO 31-0, i.e. the comma [,] or full stop [.]. Of these,
> the comma is the preferred sign
>

I noticed this issue because a script I wrote used the unix `date` command
to generate a timestamp (later fed into PostgreSQL)

> $ date --iso-8601=ns
> 2025-10-10T10:38:59,386724473+11:00

I read over the documentation for Date/Time types:
https://www.postgresql.org/docs/18/datatype-datetime.html

> Date and time input is accepted in almost any reasonable format, including
> ISO 8601

but there is no clarification on this page that the comma is not supported
as the decimal separator.

Thanks,
Zane