Question regarding the "all" property

I'm writing about the new "all" property and I just wanted to make sure I'm
factually correct on a few points:

"all" is just a regular CSS property and all the normal specificity rules
of the cascade apply, correct?

That means that if I've done something like:

#sidebar > div { background: red; }

Then the following rule, if applied to a <div> in the sidebar will not
override the previous background definition.

.widget { all: default; }

If so, that implies that the all property cannot be used to achieve true
encapsulation, it's just a simple way for authors to undo what they've
already done (no judgment either way, just checking).

Am I'm understanding this correctly?