Root Inline Box - Can an root inline box have descendants in turn or what does that mean?

https://www.w3.org/TR/css-inline-3/#root-inline-box

> The block container also generates a root inline box, which is an
> anonymous inline box that holds all of its inline-level contents.
> (Thus, all text in an inline formatting context is directly contained
> by an inline box, whether the root inline box or one of its
> descendants.) The root inline box inherits from its parent block
> container, but is otherwise unstyleable.

What does "one of his descendants" refer to?

Can an root inline box have descendants in turn or what does that mean?

Let's suppose we have this mark-up

<div>
  In the case of <strong>Fire</strong>, break glass to 
  <span>sound alarm. <img src="bell.jpg" alt="bell symbol"></span>
</div>

This will generate a box tree.

"Fire" and "sound alarm" are contained within boxes that are descendants of the root inline box, while "In the case of " and " break glass to " are contained directly by the root inline box.