str methods: upper or lower

To answer this question, search through Python documentation of str for methods that could be useful in your solution. Complete this function according to its docstring description.

def upper_lower(text: str) -> bool: """Return True if and only if there is at least one alphabetic character in text and the alphabetic characters in text are either all uppercase or all lowercase.

>>> upper_lower('abc')

True

>>> upper_lower('abcXYZ')

False

>>> upper_lower('XYZ')

True

"""