The regular expression:

(?-imsx:\\\\(?:[a-zA-Z0-9]+\\)+[a-zA-Z0-9]+)

matches as follows:
  
NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  \\                       '\'
----------------------------------------------------------------------
  \\                       '\'
----------------------------------------------------------------------
  (?:                      group, but do not capture (1 or more times
                           (matching the most amount possible)):
----------------------------------------------------------------------
    [a-zA-Z0-9]+             any character of: 'a' to 'z', 'A' to
                             'Z', '0' to '9' (1 or more times
                             (matching the most amount possible))
----------------------------------------------------------------------
    \\                       '\'
----------------------------------------------------------------------
  )+                       end of grouping
----------------------------------------------------------------------
  [a-zA-Z0-9]+             any character of: 'a' to 'z', 'A' to 'Z',
                           '0' to '9' (1 or more times (matching the
                           most amount possible))
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------