Returns 1 if the position number of the given part is the same as the position number of the main part in the assembly.
To show a main part of an assembly on top of part lists:
In the Template Editor, add value field SIMILAR_TO_MAIN_PART to PART row.
Set the Order to Descending and (if needed) hide the field in output, in the Value Field Properties dialog box.
Drag the SIMILAR_TO_MAIN_PART field to be first in sort order in the Content browser.