== Make inline region semantics set values on current region ==
The current semantic when inline style attributes applicable to
regions are used in content elements is to create a new implied inline
1. Keep existing semantic where new anonymous regions are created.
2. Modify the semantic such that when region style attributes are
encountered on content elements they are used to modify the current
region for that content element while the element is active.
Option 2 would be syntactic shorthand for a `<set>` element on a
region that modifies the region's `tts:origin`, `tts:extent` or