Import from main repo
<layout> seems a good place to collect general information about the appearance of ruby (left right top bottom), so as to not repeat the @place on every <rt>, <div>, <p>… . In my experience, where ruby appear is a document property, no need to insert into more low level markup. Do we want to give <layout> a special section to specify rt appearance, and the number of ruby streams. I m leaning towards yes.