This feature allows a user to repeat the operator any number of times required. This is fundamentamental when using snap points for placing a number of objects with precision.
It works for all transforms, but it really make sense on duplicate operations or when adding data using a transform, eg extruding.
It differs from Repeat Operator (SHIFT+R) in the sense that operator is restarted with user input.
Changes on source are isolated via WITH_MECHANICAL_TRANSFORM_MULTIPLE and WITH_MECHANICAL compiler definition
A new return code for operator is defined: OPERATOR_REPEAT
Low level changes are performed on wm_event_system.c , allowing it to be used in other places if needed.
When opeator is a macro (eg, copy with translation) the last element is duplicated. This is because to finish the multiple operator the last one is cancelled, not considering the parent.