This is a reference to Jaʿfar al-Ṣādiq's agreement with the various legal opinions of the jurists of Mecca, Medina, and Iraq on some questions. Hossein Modarressi employs this reference to show the extent to which Jaʿfar was aware of the differing legal views of his time.
This source is part of the Online Companion to Hossein Modarressi, Text and Interpretation: Imam Jaʿfar al-Ṣādiq and His Legacy in Islamic Law (Harvard University Press, 2022).