The small #elisp linked below demonstrates how to limit the completion of certain commands to a specific major mode in #emacs E.g. to make ledger-occur only available when you’re in a buffer with ledger-mode.
Packages which define (interactive) commands may handle this themselves. See the MODES argument in the (interactive) help text. However, it’s not a common practice, so you can achieve this from your own configuration with a few lines of elisp.
Why do this? I maintain my ledger in an #orgmode file with ledger source blocks in between. ledger-occur does not behave well when used in a different mode, and it resulted in data loss when executed in an Org buffer. To prevent accidentally selecting ledger-occur in other contexts, I put a restriction in place:
(my/restrict-symbol ‘ledger-mode ‘(ledger-copy-transaction-at-point ledger-occur))
Now, I can’t accidentally invoke ledger-occur or ledger-copy-transaction-at-point outside ledger-mode.
The restriction only affects the completion options in the command list invoked by M-x. Therefore, if you bind a restricted command to a key, it would still be invokable.