A Continuation is used in seq and alt Combined Fragments, to indicate the branches of continuation an operand follows. To indicate a continuation, end an operand with a Continuation, and indicate the continuation branch with a matching Continuation (same name) preceding the Interaction Fragment. 

You create a Continuation by dragging the State/Continuation element onto the diagram from the Interaction Elements page of the Enterprise Architect UML Toolbox.

For the following continuation example, an alt Combined Fragment has Continuations pathSucc and pathFail. These Continuations are located within the Interaction Occurrence ConnHandler, which has subsequent events based on the continuation. 

Below is the interaction referenced by the Interaction Occurrence.

OMG UML Specification

The OMG UML specification (UML Superstructure Specification, v2.0, p. 414) states:

"A Continuation is a syntactic way to define continuations of different branches of an Alternative CombinedFragment. Continuations is intuitively similar to labels representing intermediate points in a flow of control."

The OMG UML specification (UML Superstructure Specification, v2.0, p. 415) also states:

"Continuations have semantics only in connection with Alternative CombinedFragments and (weak) sequencing. If an InteractionOperand of an Alternative CombinedFragment ends in a Continuation with name (say) X, only InteractionFragments starting with the Continuation X (or no continuation at all) can be appended."