What is the meaning of the re.DEBUG flag?

The re.DEBUG flag offers a peek at the inner workings of a regular expression pattern in Python, for example:

import re

re.compile(r"(a(?:b)){1,3}(c)", re.DEBUG)

Returns:

MAX_REPEAT 1 3
  SUBPATTERN 1 0 0
    LITERAL 97
    LITERAL 98
SUBPATTERN 2 0 0
  LITERAL 99

 0. INFO 4 0b0 3 7 (to 5)
 5: REPEAT 11 1 3 (to 17)
 9.   MARK 0
11.   LITERAL 0x61 ('a')
13.   LITERAL 0x62 ('b')
15.   MARK 1
17: MAX_UNTIL
18. MARK 2
20. LITERAL 0x63 ('c')
22. MARK 3
24. SUCCESS

Where can I find the meaning of the OPCODES (SUBPATTERN, MAX_REPEAT, etc.)? Some of them are self-explanatory, but the whole purpose is unclear. What does 1 0 0 means in SUBPATTERN 1 0 0?

Some things I've tried:

• Read the docs on re.DEBUG
• Read the source code of the parser.
• Google search

Note: I know that perhaps this is not a perfect fit for a StackOverflow question, but I've written a clear problem with an MRE and my efforts at solving the issue at hand. Moreover, I think having this solved benefits the other users as well.

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