General format of the 'show' command:
    vitis show -c|-e|-v <input data> [options]

---

vitis show -c <category> [options]
    Displays files that belong to the specified category.
    Shows categories and files located in the category root.
    Example:
        vitis show -c "Disco 80's"

---

vitis show -e <expression> [options]
    Displays files according to an expression
    with the operations of intersection, union, complement (difference).
    Operation designations:
      +--------------+----+---+
      | union        | u: | : |
      | intersection | i: | % |
      | difference   | d: | - |
      +--------------+----+---+
    The grouping of parts of an expression is performed using square
    brackets or braces (square brackets are recommended). All components
    of an expression (including brackets) are separated by spaces.
    Examples:
        vitis show -e category1 : category2 : category3
            Displays all files from three categories.
        vitis show -e category1 u: category2 u: category3
            Produces the same result.
        vitis show -e category1 % [ category2 : category3 ]
            Takes the union of category2 and category3
            and intersects them with category1.

---

vitis show -v <file> ... [options]
    Displays the specified files relative to the Vitis mount point.

---

vitis show --by-relations [--name|-R <relation_name>] \
                          [--direction|-W <direction>] \
                          [--target|-B <file>] \
                          [options]
    Find and display all files with relations by these parameters:
    relation name, relation direction, related file.
    Each parameter is optional.
    Direction variants:
        ":"  - to right;
        ":-" - to left;
        "-"  - birectional.
    Examples:
        vitis show --by-relations
            Display all files which have any relations.
        vitis show --by-relations -D ":" -B "Literature/"
            Display file list with directonal relation
            to the "Literature" category; relation name does not matter.

---

> Options for all variants of the command:

    --categories enables displaying categories of output files;
    --details enables displaying file properties;
    --relations enables displaying relation lists of files;
    --relation-details enables displaying an additional
      information about relations;
    --full-details does the same
      as using the --categories, --details and --relations together;
    --tags enables displaying tags of output files;
    --xattrs option enables displaying extended attributes;
    --json enables displaying data as JSON;
    --dialog (or -D) enables experimentaul TUI mode;
    --use-canon-name enables displaying canon names of files instead of their
      paths; this makes the most sense with 'vitis show -v'.

---

> Opening and execution.

With the '--open' option, files are opened using the 'ufo' utility.

You can specify another program instead of 'ufo'
using '--app <program>'.

With the '--run' option, files are executed as programs (if they have
the appropriate permissions).

---

> Options affecting the file list to be created (relevant for -c and -e).

The '-n' option is used to select one or more specific files.
If a single number follows the '-n' option, only that file will be displayed.
You may also use an expression consisting of item numbers and ranges
separated by commas (without spaces). Ranges are specified with hyphen (-).
Single numbers and ranges may be mixed in the same expression.
Examples:
    vitis show -c Music -n 4-13,18,24-31
        Displays files 4 through 13 inclusive, file 18,
        and files 24 through 31 inclusive.
    vitis show -c Books -n 1
        Displays the first file in the 'Books' category.

The --sort=<sorting> option specifies the sorting type:
    --sort=extension - sort by file extension;
    --sort=name      - sort by file name (default);
    --sort=none      - no sorting;
    --sort=size      - sort by file size;
    --sort=time      - sort by file modification time;
    --sort=atime     - sort by file access time;
    --sort=mix       - random order.

The '--reverse' or '-r' option reverses the sort order.
