This reads to me like [OR] is optional and means the same without [OR] with a space separator, so I interpret it as: <logical-expression> [OR] <logical-expression> is equivalent to <logical-expression> <logical-expression>
Am I not understanding this syntax in Reference correctly?
I think you're indeed misinterpreting that syntax. When no operator is specified, AND is implied. I do agree that this can be a little confusing. You might want to post that as a feedback at the bottom of the docs page, such that the author of that page can perhaps clarify that.