m/
      www     # match literal 'www'
      .       # match any single character except \n.
      [a-z]   # match any single character between a and z.
  |           # OR
      [A-Z]   # match any single character between A and Z.
      .       # match any single character except \n.
      [a-z]   # match any single character between a and z.
/ix           # /i makes everything case-insensitive, so there's
              # no difference between [A-Z] and [a-z].