[Uncle Timmy]
> Would have to look at the history to see who added it, and ask them. 

That would be me :-)

At the time, the goals were to:

1) make an easy-to-use, readable output format for file comparisons,

2) use the unmodified output of the existing SequenceMatcher(None,a,b).get_grouped_opcodes(n) method,

3) create output that works with patch and ed, and

4) comply with the output format spec in the Single Unix Specification found at http://www.unix.org/single_unix_specification/ . See the attached excerpt.

No effort was made to exactly reproduce the output of GNU diff.  It was just an alternate output format for the SequenceMatcher.