Why does the PresenceState contain a list of Presence for each entry?

The type is:

export type PresenceState = { [key: string]: Presence[] }

export type PresenceState = { [key: string]: Presence[] }

I tried it, and when I open multiple windows, it just adds a new entry in the

PresenceState

PresenceState

Object, so why is there a list of

Presence[]

Presence[]

for each key?