ining :class:`Word` expressions, using range notation from
    regular expression character sets.

    A common mistake is to use :class:`Word` to match a specific literal
    string, as in ``Word("Address")``. Remember that :class:`Word`
    uses the string argument to define *sets* of matchable characters.
    This expression would match "Add", "AAA", "dAred", or any other word
    made up of the characters 'A', 'd', 'r', 'e', and 's'. To match an
    exact literal string, use :class:`Literal` or :class:`Keyword`.

    pyparsing includes helper strings for building Words:

    - :class:`alphas`
    - :class:`nums`
    - :class:`alphanums`
    - :class:`hexnums`
    - :class:`alphas8bit` (alphabetic characters in ASCII range 128-255
      - accented, tilded, umlauted, etc.)
    - :class:`punc8bit` (non-alphabetic characters in ASCII range
      128-255 - currency, symbols, superscripts, diacriticals, etc.)
    - :class:`printables` (any non-whitespace character)

    ``alphas``, ``nums``, and ``printables`` are also defined in several
    Unicode sets - see :class:`pyparsing_unicode``.

    Example::

        # a word composed of digits
        integer = Word(nums) # equivalent to Word("0123456789") or Word(srange("0-9"))

        # a word with a leading capital, and zero or more lowercase
        capital_word = Word(alphas.upper(), alphas.lower())

        # hostnames are alphanumeric, with leading alpha, and '-'
        hostname = Word(alphas, alphanums + '-')

        # roman numeral (not a strict parser, accepts invalid mix of characters)
        roman = Word("IVXLCDM")

        # any string of non-whitespace characters, except for ','
        csv_value = Word(printables, exclude_chars=",")
    NF)