I printed coreutils manual -221pages, and found out that most programs that accept long options recognize unambiguous abbreviations of these options.

for example:
rmdir --ignore-fail-on-none-empty
can be entered simply as rmdir --i
But this is only because there was no other option starting with 'i'. Let us look what would happen if there was. e.g. there are --verbose and --version options. If I enter
rmdir --v
I get
rmdir: option '--v' is ambiguous.