The function applies a Caesar cipher with a fixed shift of 6 on the input string, leaving non-alphabetic characters unchanged.
[CODE]:
```python
def caesar_cipher(text, shift=6):
    result = []
    for char in text:
        if char.isalpha():
            shift_amount = shift % 26
            if char.islower():
                result.append(chr((ord(char) - ord('a') + shift_amount) % 26 + ord('a')))
            else:  # char.isupper()
                result.append(chr((ord(char) - ord('A') + shift_amount) % 26 + ord('A')))
        else:
            result.append(char)
    return "".join(result)
```