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%r{
      \(                                            # Literal paren
              [ ]*                         # Zero or more spaces
              <?(.+?)>?                    # URI = $1
              [ ]*                         # Zero or more spaces
              (?:                                  # 
                      ([\"\'])            # Opening quote char = $2
                      (.*?)                       # Title = $3
                      \2                          # Matching quote char
              )?                                   # Title is optional
      \)
}x