"""Calculate the normalized Levenshtein edit distance between two strings.

This function computes the difference rate between two strings based on the Levenshtein edit distance,
normalized by the maximum length of the two strings. The result is a float in the range [0, 1], where 0
indicates that the strings are identical, and 1 indicates that they are completely different.

Args:
    text1 (str): The first string to compare.
    text2 (str): The second string to compare.

Returns:
    float: The normalized difference rate between the two strings, ranging from 0.0 (identical) to 1.0 (completely different).

Note:
    The Levenshtein edit distance is the minimum number of single-character edits (insertions, deletions, or substitutions)
    required to change one string into the other. The normalization ensures that the result is independent of the string lengths.

Examples:
    >>> calculate_diff_rate('hello', 'hello')
    0.0
    >>> calculate_diff_rate('abc', 'def')
    1.0
    >>> calculate_diff_rate('abc', 'abcd')
    0.25
    >>> calculate_diff_rate('abcd', 'abc')
    0.25
    >>> calculate_diff_rate('abc', 'ab')
    0.3333333333333333
"""