Re: Some minor suggestions to Tab Bar

[Juri Linkov]

> 2. Add new faces for group tabs. The idea is to differentiate these 2
> cases:
>   2.1. Tabs from the current group X tabs from other groups
>   2.2. Regular tabs X collapsed group tabs
>
> It's not possible to know which tabs belongs to the current group or
> which tabs represent another group, since all inactive tabs use the same
> face 'tab-bar-tab-inactive'. I did a slight modification to
> 'tab-bar-tab-name-format-default' and 'tab-bar-tab-group-format-default'
> to add two new faces:
>
> In the example above (please desconsider the styles I used), we can see
> that:
>   * [1], [2] and [8] are tabs that do not belong to any group (ungrouped)
>   * [3] is a collapsed group tab of a group named "group1", where tab
>     [4] belongs to the same group and is hidden
>   * [5] and [7] are tabs that belongs to the current group (same group)
>   * [6] is the current active tab

As a first stab at tab faces, now there are 3 new faces:

- tab-bar-tab-group-current
- tab-bar-tab-group-inactive
- tab-bar-tab-ungrouped

and two new options:

- tab-bar-tab-face-function
- tab-bar-tab-group-face-function

The latter can be used for color-coding, e.g. by assigning a distinctive
color to each group of tabs.

I'm striving to make only minimal changes in the core library
and to provide enough knobs for easy customization.

Please try this to see if there is still anything missing.