A structure to hold a logical document position that can be converted to a raw document position or an x-y position.

A document position can specify a leading or trailing edge or a text directionality so that bidirectional hit testing can use both these distinctions.

The leading edge at position N is the position before character N in logical order, and the trailing edge is the position after character in logical order.

Specification by directionality works differently. Character N in left-to-right text is preceded by position N (left-to-right) and followed by position N+1 (left-to-right). Character N in right-to-left text is preceded (in display order) by position N+1 (right-to-left) and followed by position N (right-to-left).