Sometimes it is useful to split out a part of either the basic flow, or another flow, so that it can be re-used within the use case. This flow is created in a separate paragraph of the use case document and 'called' just as a sub-function would be called if we were writing code.

	The sub flow paragraph is given the title: "Sub-Flow: XXX", where XXX the name of the sub-flow starting with an active verb.
	In the calling flow the sub-flow is invoked by referring to its name. In the example the words of the title of the sub-flow are capitalised to indicate the call. Other forms include: 'The sub-flow XXX runs here' or 'Do sub-flow XXX' which may be starting to look too much like code for non-technical users.
	The sub-flow always runs and returns to the point from which it was invoked, unless an exception during the sub-flow prevents it from returning. The use case then continues from that point.
	The sub-flow can also be used to provide alternative paths following a case statement or other selection statement if this is deemed more appropriate than using one or more alternate flows.