Understanding command line documentation synopses – or/optional/and?

Is there documentation for the documentation for gcloud commands? At the moment I’m inferring what the various formatting and symbols probably mean in the Synopsis section of the gcloud documentation (https://cloud.google.com/sdk/gcloud/reference/). For example, what does the pipe mean here: ‘gcloud GROUP | COMMAND [–account=ACCOUNT] ….’? Is something in square brackets optional?