# Matches ANSI Underline/DoubleUnderline Start or Underline End
\e                             # An Escape
\[                             # Followed by a bracket
(?>
  (?<UnderlineStart>4m)        # 4m starts underline
  |
  (?<DoubleUnderlineStart>21m) # 21m start a double underline
  |
  (?<UnderlineEnd>24m)         # 24m stops underline
)