CJK 1.7: story direction belongs to the story

Vertical is a story property: every frame of a thread is vertical or
horizontal together, a frame threaded onto a story takes its direction,
and frames split off by threading or breaking a thread keep theirs.
Type > Story Direction is type.storyDirection {vertical} (checked in the
menu) for the stories of the text selection or selected frames;
object.textFrameOptions {vertical} and frame.create {vertical} set the
frames' stories. Documents that stored Vertical on the frame open with
each story taking its first frame's direction. IDML StoryOrientation is
read into and written from the story, beside its column direction
(StoryDirection), which stays a separate setting.

docs/cjk.md

@@ -31,7 +31,7 @@ presets or tables are copied. Our default mojikumi and kinsoku tables are built
 
 | Area | State |
 |---|---|
-| Vertical frames, upright CJK, rotated Latin | done (per frame; glyphs turned by transforms) |
+| Vertical text, upright CJK, rotated Latin | done: story direction per story (frames of a thread agree; IDML `StoryOrientation`); glyphs turned by transforms |
 | Vertical metrics and shaping | done: upright runs shaped top to bottom (`vert`; `vkrn`/`vpal` when asked) with `vmtx`/`VORG` advances and origins, centred on the ideographic em box (`BASE`, else OS/2); turned runs shaped horizontally, without `vrt2`; Horizontal Kana (`hkna`) takes the vertical kana (`vkna`) in upright runs. Default location of variable fonts only (no `VVAR`) |
 | Kinsoku | named (hard, soft, Chinese, Korean) and custom kinsoku sets, bunri-kinshi, rensuuji, hanging punctuation (regular, force); without a set, fixed no-start / no-end lists and a break anywhere between CJK characters; kinsoku type (push in / push out priorities) kept but not applied |
 | Korean line breaking | at spaces (Hangul everywhere, hanja in Korean text); per-paragraph character-based breaking (`koreanCharBreaks`); DesignCraft-only, not in IDML |
@@ -105,8 +105,7 @@ working (tsume removes the side bearings before mojikumi runs).
   shaper reports vertical advances; rotated (Latin) runs stay horizontal and turn as a whole.
   `vrt2` only for runs that are rotated, never with an extra turn.
 - Glyph placement in vertical lines uses the vertical origin, not a guessed centre.
-- Story direction per story (IDML `StoryOrientation`) rather than per frame; frames of one story
-  agree.
+- Story direction per story (IDML `StoryOrientation`); frames of one story agree.
 - Arrow keys and carets follow the vertical line direction.
 
 ### Annotations and inline structures