Merges flow variables into one stream. This node aggregates variables defined in different input connections into one variable connection. It does not modify variables but only merges them. Note, if there are the same variables defined in different inputs, the standard conflict handling is applied: Top most inputs take priority and define the value of a variable. This node can also be used as a common barrier point to control the execution order of nodes, i.e. nodes connected to the output port will not start executing until all upstream nodes have been executed.