Wild cards on Assist message can be used in two ways.
Wild card for Protocol
You can use the wild card for the protocol as shown below
e.g. - *://www.jstor.org. if you set an Assist message with * as the protocol, Assist message will pop up for both HTTP & HTTPS protocols.
Wild card for domain
You can set up an Assist message with a wild card included in the domain.
e.g. - If you set up an Assist message to *.bjm.com, extension will show the Assist message on journals.bjm.com, Bjo.bjm.com.
But the Assist message will not pop up on bjm.com (main page).