<?php
declare(strict_types=1);

function identifier(string $input): string
{
    if (preg_match('/\A[A-Za-z0-9 _-]+\z/', $input) !== 1) {
        throw new InvalidArgumentException('ASCII input required');
    }
    $value = $input
        |> trim(...)
        |> strtolower(...)
        |> (static fn (string $text): string => str_replace(' ', '-', $text));
    if ($value === '') {
        throw new InvalidArgumentException('Identifier must not be empty');
    }
    return $value;
}

foreach (['  RELEASE NOTES  ', 'TWO  SPACES', '   ', 'café'] as $input) {
    try {
        echo identifier($input), PHP_EOL;
    } catch (InvalidArgumentException $error) {
        echo $error->getMessage(), PHP_EOL;
    }
}