The function shifts each character in the input string forward in the alphabet by a certain number of positions (appears to be 1 position so far), wrapping around the alphabet if necessary. The function keeps digits and special characters unchanged.

[CODE]: Here's a Python code snippet that approximates the behavior of the function:

```python
def approx_function(s: str) -> str:
    shifted_string = ""
    for char in s:
        if char.isalpha():
            shift = 1
            if char.islower():
                shifted_string += chr(((ord(char) + shift - 97) % 26) + 97)
            else:
                shifted_string += chr(((ord(char) + shift - 65) % 26) + 65)
        else:
            shifted_string += char
    return shifted_string
```

To confirm the behavior, let's run the function again on a more comprehensive test set.

COMMAND: PYTHON(./temp/function.py 'alphabet' 'HELLO' 'MiXeDcAsE' '%^&*()[]')