Hi all - I'm looking at the lightning design system notifications documentation (https://www.lightningdesignsystem.com/guidelines/messaging/components/notifications/)  --  specifically I'm looking at the Usage section, for when notification happen.  There is a bullet point that says:

• Custom criteria. An item meets the custom criteria set by the user.e.g. let me know when this opportunity reaches “negotiation” stage.

I can't find any other documentation on how a user can do this.  Can anyone point me in the right direction?  Thanks!