X<name> [node]* <Sub-circuit name> [PARAMS: <<name> = <value>>*]
X calls the Sub-circuit <Sub-circuit name>. <Sub-circuit name> must somewhere be defined by the .SUBCKT and .ENDS command. The number of nodes (given by [node]*) must be consistent. The referenced Sub-circuit is inserted into the given circuit with the given nodes replacing the argument nodes in the definition. Sub-circuit calls may be nested but cannot become circular.