The whitebox template is a structured means of specifying or describing whiteboxes. It contains the following elements (required information shown in bold, the rest is optional):

Part Explanation 
Diagram Shows the contained blackboxes plus their relationships
Rationale The reason why this whitebox is structured like it is.
Contained blackboxes  Names and responsibilities of contained blackboxes, plus references to their detailed description.
Internal relationships (interfaces) Brief description of the (important) relationships between internal blackboxes, plus references to their detailed description.
Risks and issues  Know issues or risks with this whitebox, information about eventual technical debt or ideas for improvement