Regex: 
  
NODE                     EXPLANATION
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  \d+                      digits (0-9) (1 or more times (matching
                           the most amount possible))
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  (                        group and capture to \1 (optional
                           (matching the most amount possible)):
--------------------------------------------------------------------------------
    .                        any character except \n
--------------------------------------------------------------------------------
    \d+                      digits (0-9) (1 or more times (matching
                             the most amount possible))
--------------------------------------------------------------------------------
  )?                       end of \1 (NOTE: because you are using a
                           quantifier on this capture, only the LAST
                           repetition of the captured pattern will be
                           stored in \1)
--------------------------------------------------------------------------------
  (                        group and capture to \2 (optional
                           (matching the most amount possible)):
--------------------------------------------------------------------------------
    [eE]                     any character of: 'e', 'E'
--------------------------------------------------------------------------------
    \d+                      digits (0-9) (1 or more times (matching
                             the most amount possible))
--------------------------------------------------------------------------------
  )?                       end of \2 (NOTE: because you are using a
                           quantifier on this capture, only the LAST
                           repetition of the captured pattern will be
                           stored in \2)