The regular expression:
(?-imsx:^.T2|S)
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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^ the beginning of the string
----------------------------------------------------------------------
. any character except \n
----------------------------------------------------------------------
T2 'T2'
----------------------------------------------------------------------
| OR
----------------------------------------------------------------------
S 'S'
----------------------------------------------------------------------
) end of grouping
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####
/^.T(2|S)/
##
##
/^.T(?:2|S)/