A data transform rule (or simply "data transform") provides a purpose-built rule for easily transforming and mapping clipboard data without using activities. In general, the data transform defines how target data (properties, pages, etc) is mapped from and transformed by source data (properties, pages, etc). These rules are instances of the Rule-Obj-Model rule type.
By convention, a data transform named pyDefault is available for most standard classes. However, the name pyDefault is not reserved and has no special significance.