This is a reference to Jaʿfar al-Ṣādiq's extensive knowledge of the range of opinions on legal matters during his time. Hossein Modarressi cites this reference in his discussion of some of the features of al-Ṣādiq's jurisprudence.
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).