Spec: Version and platform checking underspecified

Currently, the "Version and platform checking" section of the typing spec is very barebones. It basically says:

Type checkers are expected to understand simple version and platform checks. [...] Don’t expect a checker to understand obfuscations like "".join(reversed(sys.platform)) == "xunil".

Of course, there's a world of difference between these two forms.

The type stubs document goes into a bit more of detail, and reflects the currently implemented functionality quite well, as far as I know. It would be a good starting point.

Maybe it would also make sense to support platform checks using startswith(), as that is officially recommended in the Python docs, and is required to properly support some Unix variants, like FreeBSD, that include the version number in the platform string. See also python/typeshed#11876.

Beginne damit, den Abschnitt „Version and platform checking“ der Typing-Spezifikation mit dem verlinkten Dokument zu Typ-Stubs zu vergleichen, das das aktuelle Verhalten widerspiegelt. Lies die im Bericht verlinkte Python-Dokumentation und das typeshed-Issue und definiere anschließend die unterstützten Prüfungen. Entscheide außerdem, ob startswith() in die Spezifikation gehört. Erledigt ist die Aufgabe, wenn die Spezifikation das beabsichtigte Verhalten bei der Versions- und Plattformprüfung präzise beschreibt.