The function takes an input string and returns a string composed of the 0-based alphabetical indices of each character in the input in words (e.g., "zero" for 0, "one" for 1, and so on).

[CODE]: 
```python
def f(x):
    alphabet = 'abcdefghijklmnopqrstuvwxyz'
    output = []

    for char in x:
        if char in alphabet:
            index = alphabet.index(char)
            output.append(str(index))

    word_output = ' '.join(output).replace('0', 'zero').replace('1', 'one').replace('2', 'two').replace('3', 'three').replace('4', 'four').replace('5', 'five').replace('6', 'six').replace('7', 'seven').replace('8', 'eight').replace('9', 'nine')

    return word_output
```