A tabId
is a unique string of text that identifies your tab.
It needs to be in a format that can be put into an HTML attribute.
The tab ID is always required to register a tab.
A tabId
must be unique to the target sheet. For example,
the character sheet can only have one "my-module-id-my-spellbook-tab" ID,
and the NPC sheet can also only have one "my-module-id-my-spellbook-tab" ID, etc.
Advice for crafting a unique tab ID:
"my-module-id-my-spellbook-tab"
The required static ID associated with a tab.