Each interaction operand is a fragment of an interaction and covers the lifelines in the combined fragment. An interaction operand contains an optional guard condition, which is also called an interaction constraint. The interaction operand runs only if the guard condition tests true.
As the following figure illustrates, an interaction operand is displayed as a rectangular in a combined fragment.
When you create an interaction operand, it appears in an expanded state. You can collapse the interaction operand to hide the operand and its associated messages and interaction fragments and to minimize the size of the combined fragment in the interaction frame.
The number of interaction operands that you can add to a combined fragment depends on the type of the combined fragment. For example, a loop, option, break, critical, negative, assert, ignore, or consider combined fragment has one operand. An alternative, weak, strict, or parallel combined fragment has two or more operands. If more than one interaction operand exists in a combined fragment, a horizontal dashed line separates the operands.