[summary][draft][part] Tabs in vim

DISCLAIMER. English language used here only for compatibility (ASCII only), so any suggestions about my bad grammar (and not only it) will be greatly appreciated.

Status: summary.
State: draft,part.
Detailed description: Some tables for illustrate <Tab>'s handling in vim. See vim help for details.

Tabs in vim {{{

    'sts' and 'sta' options {{{

        Following options affect <Tab>s and indents:

            'tabstop'       'ts'
            'shiftwidth'    'sw'
            'softtabstop'   'sts'
            'smarttab'      'sta'
            'expandtab'     'et'

        'sw' and 'ts' define standard vim operations behavior, they are not
        switches for some features (hence they're always set and always used).
        But 'sts' and 'sta' enables additional features, which affect (change)
        some vim operations behavior (hence, they can be unset to turn feature
        off).

        Table below shows what option will be used to determine how many
        positions insert or delete during some editing operations depending on
        activated modes: both 'sts' and 'sta' are off (default), 'sts' set,
        'sta' set and both 'sts' and 'sta' set. When editing operation insert
        less (or more) positions, than real <Tab> counts for, mix from spaces
        and real <Tab>s are used.


    +--------------------------+-------------------------------------------+
    |    Operation             |   Will be inserted .. positions           |
    |                          +------+-----------+-----------+------------+
    |                          |      | +sts      | +sta      | +sts +sta  |
    +--------------------------+------+-----------+-----------+------------+
    | Use >> , etc             |  sw  | sw        |  sw       |  sw        |
    +--------------------------+------+-----------+-----------+------------+
    | Type <Tab> or <BS>       |  ts  | sts (mix) |           |            |
    |                          +      +           +-----------+------------+
    |     at the start of line |      |           |  sw (mix) |  sw (mix)  |
    |                          +      +           +-----------+------------+
    |     in other places      |      |           |  ts       |  sts (mix) |
    +--------------------------+------+-----------+-----------+------------+
    | Real <Tab> length        |  ts  | ts        |  ts       |  ts        |
    +--------------------------+------+-----------+-----------+------------+

    }}}
    ':retab' and changing 'ts' option value {{{

        'ts' option changes real tabstop, but does not change text. Hence,
        indents, which made according to old tabstop, probably will be messed
        (i.e there will be visible changes in text), but actual file remains
        untouched. So, using 'undo' after changing 'ts' has no sense.

        :retab command changes both 'ts' option and text according to new 'ts'
        value in such way, that all indents remain the same (there will be no
        visible changes), though actual file will be changed (to preserve
        visible indents :retab pads them, if necessary, with spaces). So,
        using 'undo' after :retab recover text to previous state, but not
        recover 'ts' to previous value, hence indents may be messed (like
        after you change only 'ts') and to recover visible text state you need
        set 'ts' to previous value. Table below summarizes that.


        +-------------------+---------------+-----------+
        |                   | Change 'ts'   | :retab    |
        +-------------------+---------------+-----------+
        | 'ts' changed?     | yes           | yes       |
        +-------------------+---------------+-----------+
        | File changed?     | no            | yes       |
        +-------------------+---------------+-----------+
        | Visible changes?  | yes           | no        |
        +-------------------+---------------+-----------+

    }}}

}}}