The legacy reader skipped `TV`, `Tv`, `Ty` and `TY` of section 15.3.4 of
the version 7 file format specification, so type set with `1 TV` opened
horizontal.
- `TV` sets a text object's writing direction. VectorCraft keeps one
direction for each text object, the one in force at its first
character, with a warning when a later character has another.
- `Ty` marks a Kumi block as a Tate-chu-yoko run, which is VectorCraft's
own mapping, and `TY` does the same in horizontal type. A `TY` block in
vertical type opens unmarked. Two blocks with nothing between them open
as one block.
- `Tv` sets Standard Vertical Roman Alignment.
All four are modal, and an operand other than 0 or 1 leaves the value as
it was.
Docs: docs/file-format-parity.md.