On Windows, Tab in modeless child windows cycles around the elements within those windows. Here is the route Tab takes in Reports:
Spellcheck is similar, although a bit more more circuitous.
The main window is sort of similar, but harder to track because of its dockable elements - IIRC that is why the Focus on. . . items in the View menu were implemented.
And this is what you see if you press Alt+space on those windows
BR