```python
"""Render a value as fixed-width unsigned binary, nibble-grouped."""


def format_bits(value: int, width: int) -> str:
    if not isinstance(value, int) or value < 0:
        raise ValueError("value must be a non-negative integer")
    if width <= 0 or width % 4 != 0 or width > 32:
        raise ValueError("width must be a positive multiple of four and not exceed 32")
    if value > (1 << width) - 1:
        raise ValueError("value does not fit in width bits")
    # Build the nibble groups from the most significant bit down and join them
    # with single spaces.
    return ' '.join(f"{value >> i & 0xF}" for i in range(width - 1, -1, -4))
```