[GNC] "Mod" field in GNUCash log file

[Henry Law]

I'm trying to sort out a baffling data problem with GNUCash and I'm
looking at the logs.  

I can get most of it, thanks to the column name record at the start,
but

   1. What do '=====START" and "=====END" signify? 
   2. What is the "mod" field (field #1); I see values of 'B', 'C', and
      'D' but can't deduce what they mean.

[GNUCash 4.8 on Linux Mint 21.]

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Henry Law                    n e w s @ l a w s h o u s e . o r g
Manchester, England