option(value='') -- (selected) --

p

p.

p
  | foo
  | bar
  |
  |
  | baz

p.
  foo


  bar
  baz

.

.
  foo


  bar
  baz

pre
  | foo
  |   bar
  |     baz
  | .

pre.
  foo
    bar
      baz
  .

.
  foo
    bar
      baz
  .