The function appears to be shifting the alphabetical characters by 1, wrapping around from "z" to "a" and "Z" to "A". The function leaves numbers and special characters unchanged.

[CODE]:
```python
def shift_alpha_characters_by_one(s):
    result = ""
    for char in s:
        if 'a' <= char <= 'z':
            result += chr(((ord(char) - ord('a') + 1) % 26) + ord('a'))
        elif 'A' <= char <= 'Z':
            result += chr(((ord(char) - ord('A') + 1) % 26) + ord('A'))
        else:
            result += char
    return result
```