Docs for IS_LENGTH

    Checks if length of field's value fits between given boundaries. Works
    for both text and file inputs.

    Args:
        maxsize: maximum allowed length / size
        minsize: minimum allowed length / size

    Examples:
        Check if text string is shorter than 33 characters::

            INPUT(_type='text', _name='name', requires=IS_LENGTH(32))

        Check if password string is longer than 5 characters::

            INPUT(_type='password', _name='name', requires=IS_LENGTH(minsize=6))

        Check if uploaded file has size between 1KB and 1MB::

            INPUT(_type='file', _name='name', requires=IS_LENGTH(1048576, 1024))

        Other examples::

            >>> IS_LENGTH()('')
            ('', None)
            >>> IS_LENGTH()('1234567890')
            ('1234567890', None)
            >>> IS_LENGTH(maxsize=5, minsize=0)('1234567890')  # too long
            ('1234567890', 'enter from 0 to 5 characters')
            >>> IS_LENGTH(maxsize=50, minsize=20)('1234567890')  # too short
            ('1234567890', 'enter from 20 to 50 characters')