You already have your answer, but here is a way to solve problems like this in the future.
Tip #9 from the Basic debugging checklist
YAPE::Regex::Explain:
The regular expression:
(?-imsx:INC[0-9]\{7\})
matches as follows:
NODE EXPLANATION
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(?-imsx: group, but do not capture (case-sensitive)
(with ^ and $ matching normally) (with . not
matching \n) (matching whitespace and #
normally):
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INC 'INC'
----------------------------------------------------------------------
[0-9] any character of: '0' to '9'
----------------------------------------------------------------------
\{ '{'
----------------------------------------------------------------------
7 '7'
----------------------------------------------------------------------
\} '}'
----------------------------------------------------------------------
) end of grouping
----------------------------------------------------------------------
