some of the printable elements in report templates would not have their own box definitions but instead use boxes from another printable elements of the same section.
use case: rectangle drawn around a text field with aut-sized box.
each element in report template gets an optional attribute "id". all non-empty ids must be unique across the template.
box elements get an optional attribute "refid". if refid is set, it's value must be an id of another box element in the same report section. for such boxes, all attributes except id and refid are ignored, and controlled element will be laid out using position and size of the referred box.