Address of the block's storage in a separate device allocation, null
for a host block. A device field type that keeps its storage behind a
raw device pointer overrides this, letting its backend reach the
storage by dynamic dispatch rather than by a type query.
Nodes of different colours represent the following:
Solid arrows point from a procedure to one which it calls. Dashed
arrows point from an interface to procedures which implement that interface.
This could include the module procedures in a generic interface or the
implementation in a submodule of an interface in a parent module.
Where possible, edges connecting nodes are
given different colours to make them easier to distinguish in
large graphs.