bug#51247: 28.0.60; Insufficient documentation of tab-bar.el internal functions

[Juri Linkov]

>> The nil value is supported only for the case when a function
>> is on the tab-bar-format list, but its return value depends
>> on some variable, and on some conditions might return nil.
>>
>> An example is tab-bar-format-history: when tab-bar-history-mode
>> is nil, then tab-bar-format-history returns nil, but it doesn't break
>> the tab bar.
>
> OK, but what I want to say is what effect do such functions have on
> the tab bar appearance when they return nil?  It sounds like you say
> that the appearance is not affected in any way in that case?

Exactly, they have no effect.