The function takes a string input, converts each character to its position in the alphabet regardless of case, and returns the positions as a space-separated string of numeric values. 'a' or 'A' has a position of 0, 'b' or 'B' has a position of 1, and so on.

[CODE]: 
```python
def f(x):
    alphabet = 'abcdefghijklmnopqrstuvwxyz'
    result = []
    for char in x:
        char_lower = char.lower()
        if char_lower in alphabet:
            result.append(str(alphabet.index(char_lower)))
    return ' '.join(result)
```

Let's test the function with an input containing special characters and spaces.

COMMAND: PYTHON(./temp/function.py "Hello, World!")