This variable may be overridden with a user-provided function to
customize help text for tabs displayed on the tab-bar. Help text
is normally shown in the echo area or via tooltips. See the
variable's docstring for arguments passed to a help-text function.

My current implementation, which fully overrides 'tab-bar--format-tab',
uses a function that returns the buffer-list for current tabs, and wc-bl
for others.

Others might find this useful if they depend on help text.

-Stephane