瑜伽師地論略纂 8.148

8.148

論初解受、心、法念住中，此中意，若緣內身，生受、心、法念，緣此受、心、法，是名內受、心、法觀。如內，外等亦爾。此中緣身，無簡能造、所造，總緣；若下第四，唯能造，非所造，故別也。

In the treatise's initial explanation of the smṛtyupasthānas on feeling, mind, and dharmas: the meaning here is that if, taking the internal body as object, mindfulness of feeling, mind, and dharmas arises, taking these feelings, minds, and dharmas as object is called contemplation of internal feeling, mind, and dharmas. As with the internal, the external and so forth are also like this. Here, taking the body as object does not differentiate between the primary elements (the producers) and the derived elements (what is produced), but takes them as object collectively; whereas in the fourth below, it is only the primary elements and not the derived elements, hence they are different.