zanbaldwin/camelCaseToSnakeCase.php

## camelCaseToSnakeCase.php
<?php

function camelCaseToSnakeCase(string $input): string {
    preg_match_all('!(^[a-z\d]+)|(?:_?)([a-z\d]+|[A-Z][a-z\d]+|[A-Z][A-Z\d]*(?=_|$|[A-Z][a-z\d]))!', $input, $matches);
    return strtolower(implode('_', array_map(function (string $part): string {
        return trim($part, '_');
    }, $matches[0])));
}
	<?php

	function camelCaseToSnakeCase(string $input): string {
	preg_match_all('!(^[a-z\d]+)\|(?:_?)([a-z\d]+\|[A-Z][a-z\d]+\|[A-Z][A-Z\d]*(?=_\|$\|[A-Z][a-z\d]))!', $input, $matches);
	return strtolower(implode('_', array_map(function (string $part): string {
	return trim($part, '_');
	}, $matches[0])));
	}