CSS Shadow Parts - examples of part="confirm-button, * => confirm-*" syntax plz

[brucelawson]

In https://tabatkins.github.io/specs/css-shadow-parts/, there is an example

"If the ’s internal confirm button had used something like part="confirm-button, * => confirm-*" to forward the button’s internal parts up into the panel’s own shadow part map, then a selector like x-panel::part(confirm-label) would select just the one button’s label, ignoring any other labels."

Suggest that the syntax "* => confirm-*" be defined and further explained; I had to ask @tabatkins on twitter how I can choose to expose that info to people consuming my custom element, as this part of spec was opaque to me and my colleagues.