Display areas

• Display areas don't occur directly in lines.
• Display area has an inherent orientation. Think of this as an arrow saying "this should align with filling direction".
• Display areas are used to fill area containers.
• Result of filling area container is area.
• Area container has filling direction. Size of area container can grow in this direction according to size of areas with which it is filled.
• Display areas are stacked in filling direction.
• Size of area container in other direction fixed.
• Filling direction of area container = placement direction of display area
• A display area is always created so that it's size in direction perpendicular to its placement direction is equal to size of area container in direction perpendicular to filling direction. This is the display size of the area.
• Area container can specify rotation to be applied to display areas before they are filled.