Special Parameters for Template Filters used in Record Selectors
If you define a template filter for a record selector, you can also add:
Parameters using Function names (with the prefix $par or $cur) that have been assigned in the source field group.
Parameter:Key function that is assigned to the new child record. If a user calls the record selector again before saving, CRM.pad does not add another new record but replaces the previous (unsaved) record.