Newbie - Outliner Highlights

What do these Outliner highlights mean? I can’t seem to predict when they will highlight or not when I click them. It’s certainly not the object selected. The highlighted type I know is the selected object.

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That is a way to select many objects to make some operations at once in the outliner, for example you can delete all of the highlighted object with key X, toggle viewport visibility with V, toggle select S, Toggle rendering R, and may be more, but i don’t know.
Cheers!

From my experiments, no the highlighted " horizontal band" does not indicate that two items are selected. The highlighted “type” does. The colored circle around the axis icon does also. I’ll keep looking and experimenting but are there any other ideas?