preamble-uint-requires

# `preamble-uint-requires`

The `requires` header is a sorted list of non-negative integers.

## Examples

    error[preamble-uint-requires]: preamble header `requires` items must be sorted in ascending order
      --> input.md
       |
    11 | requires: 20, 1337, 86
       |

    error[preamble-uint-requires]: preamble header `requires` items must be unsigned integers
      --> input.md:11:10
       |
    11 | requires: 20token
       |          ^^^^^^^^ not a non-negative integer
       |

## Explanation

`preamble-uint-requires` ensures that the `requires` front matter (or preamble) field value contains only non-negative numbers, and that those numbers are sorted in ascending order.

Keeping a consistent order for lists makes it easier to find particular values.