Acts like a temporary table which can either be altered by (almost) every instruction within a transformation script or by some import instructions (Excel, XML, ZIP, etc.) upon import.
All instructions can be used to create subtables from the current state of a transformation script by adding the subtable key with a custom label "subtable" : "label_of_subtable". The new subtable will then hold the current state with the given instruction applied.
All other instructions can then be applied on that subtable like any regular table.
Further it is possible to create multiple subtables within a single transformation script. Please be aware that this might increase processing time.