DrawFBP supports "stepwise decomposition", a term that refers to
starting at the top of a design, sketching it out, and then
progressively filling in each block with lower level processes.
This process may proceed through several levels.
As described above, if a block on the diagram is associated with
another diagram, it will be displayed with a doubled
border. Double clicking on this block will bring up the
lower level diagram in another tab. The higher level diagram is
retained, and may be accessed via an earlier tab.
The lower level diagram(s) will usually have "sticky" connections,
shown using the External Port icon.
A subnet can be created either by creating a normal block and associating a subnet with it, using "Select Subnet Diagram",
or by selecting the Subnet button at the bottom of the screen, and clicking somewhere on the screen,
as you would for a normal block.