yes. that's why i wrote it in '['-brackets.
but usually, in info-documents a synopsis is written about it.
I think that it's not self-evident, that "you can either give a file or let the tool read from stdin or output to stdout" and therefore should be written explicitly.

In the texinfo document, which is opened, when invoking 'info gnupg', there is a subchapter called "Invoking GPG". In this chapter, commands and options are defined. This is the text I mean.