I don't fully understand the use of "so" at the beginning of a clause.
We can use "so" at the beginning of a clause with "say", "hear", "understand", "tell", "believe", and a number of other verbs. This structure is used to say how the speaker learned something.
- It's going to be a cold winter, or so the newspaper says.
- Mary's getting married. ~ Yes, so I heard.
- The Professor's ill. So I understand.
I can get all that there has been asserted but for the bold part.