to leave linejunk None; the underlying SequenceMatcher class has
  an adaptive notion of "noise" lines that's better than any static
  definition the author has ever been able to craft.

- `charjunk`: A function that should accept a string of length 1. The
  module-level function `IS_CHARACTER_JUNK` may be used to filter out
  whitespace characters (a blank or tab; **note**: bad idea to include
  newline in this!).  Use of IS_CHARACTER_JUNK is recommended.
NŠ