```python
def hex_groups(values: list, width: int) -> str:
    if not isinstance(values, list):
        raise ValueError("The first argument must be a list.")
    if not all(isinstance(v, int) and 0 <= v <= 255 for v in values):
        raise ValueError("All elements in the list must be integers from 0 to 255.")
    if not isinstance(width, int) or width <= 0:
        raise ValueError("The width must be a positive integer.")
    
    groups = [values[i:i+width] for i in range(0, len(values), width)]
    hex_groups = [''.join(f'{b:02x}' for b in group) for group in groups]
    
    return ' '.join(hex_groups)
```