def _ParsePlusMinusList(value):
  """Parse a string containing a series of plus/minuse values.

  Strings are seprated by whitespace, comma and/or semi-colon.

  Example:
    value = "one +two -three"
    plus = ['one', 'two']
    minus = ['three']

  Args:
    value: string containing unparsed plus minus values.

  Returns:
    A tuple of (plus, minus) string values.
  """
  plus = []
  minus = []
  # Treat ';' and ',' as separators (in addition to SPACE)
  for ch in [',', ';']:
    value = value.replace(ch, ' ')
  terms = [i.strip() for i in value.split()]
  for item in terms:
    if item.startswith('-'):
      minus.append(item.lstrip('-'))
    else:
      plus.append(item.lstrip('+'))  # optional leading '+'

  return plus, minus