Return initial letters of words

initials.php

<?php

/**
 * Returns initial letters of all words from all arguments.
 *
 * @param $string $str,...
 * @return string
 * @example initials('Johann Sebastian', 'Bach') => 'JSB'.
 */
function initials()
{
    // qv stackoverflow.com/questions/9706429

    $args = implode(' ', func_get_args());

    // use lookbehind to find all Unicode letters preceded by word boundary
    preg_match_all('/(?<=\b)\p{L}/', $args, $matches);

    $initials = implode('', $matches[0]);

    return strtoupper($initials);
}