This is a reference to Jaʿfar al-Ṣādiq's extensive knowledge of the differing legal opinions of his time as well as points of consensus. Hossein Modarressi employs this reference to show how Jaʿfar disagreed with jurists of other regions on some legal questions.
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).