```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 not isinstance(width, int) or 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.bit_length() > width:
        raise ValueError("value does not fit in width bits")
    return ' '.join(f'{value >> i & 0xF:04b}' for i in range(width - 1, -1, -4))
```