Ionic v4: Main attribute in router-outlet not documented

I’ve used the ionic menu in my app–which in the first place, didn’t swipe–so I’ve read some of the documentation of Ionic and saw, that they added an attribute main to the ionic-router-outlet.

This also just works if the menu is not encapsulated into it’s own component. I have to write it down among the router-outlet in the app.component.html

What makes me curious is, that this property “main” on the router-outlet component is not documented at all. At least I didn’t find it.

Also, here is the example, where the property has been used: (which looks like this: <ionic-router-outlet main></ionic-router-outlet>

Last but not least I want to apologize if I overlooked something–this is my first Ionic app ever-- and I want to thank anybody who helps me solving this problem

Kind Regards

EDIT: It’s not worthy at all but I forgot to post my menu code. It’s really nothing special and almost 1:1 copied.

<ion-menu menuId="sideMenu" swipeGesture="true">
    <ion-toolbar color="primary">
      <ion-button slot="start">
        <img alt="logo" src="../../assets/logo.svg">
        app name