Pattern for transforming list items

%r{
      (\n)?                                                 # leading line = $1
      (^[ ]*)                                                       # leading whitespace = $2
      (#{ListMarkerAny}) [ ]+                       # list marker = $3
      ((?m:.+?)                                             # list item text   = $4
      (\n{1,2}))
      (?= \n* (\z | \2 (#{ListMarkerAny}) [ ]+))
}x