Show content if logged in user is in userGroup1 OR userGroup2? This is so simple in ExpressionEngine and yet I've tried everything for several hours and can't find a way to get it working in Craft???

I have 2 User Groups: userGroup1, userGroup2

If the currently logged-in User belongs to either of those groups, show them "==SECRET CONTENT==" that guests (not logged-in users) do not see. 

The following IF will only show "==SECRET CONTENT==" to userGroup1:

{% if currentUser and currentUser.isInGroup('userGroup1') %}
    ==SECRET CONTENT==
{% endif #}


Now, based on everything I've found and read, it would seem the following SHOULD show ==SECRET CONTENT== to Users belonging to EITHER userGroup1 OR userGroup2:

{% if currentUser and currentUser.isInGroup('userGroup1','userGroup2') %}
    ==SECRET CONTENT==
{% endif #}


But it only shows ==SECRET CONTENT== to userGroup1. And if I switch the isInGroup values to the following, only userGroup2 see the ==SECRET CONTENT==

{% if currentUser and currentUser.isInGroup('userGroup2','userGroup1') %}
    ==SECRET CONTENT==
{% endif #}


I've tried Group IDs. I've tried every variation of formatting, array syntax, etc. 
I've searched the docs and StackExchange dozens of times...  

How can I display "==SECRET CONTENT==" to users belonging to userGroup1 OR userGroup2 ??
According to the docs, the userModel.isInGroup() method takes a "user group model, its handle, or ID" – in other words, it can only test for membership in a single group, not several.

What you want in this case is the or operator:

{% if currentUser and (currentUser.isInGroup('userGroup1') or currentUser.isInGroup('userGroup2')) %}
    {# secret content #}
{% endif %}