How to extract a file extension in PHP?

PARSE_URL documentation

$x = parse_url('http://example.com/myfolder/sympony.mp3?aa=1&bb=2?cc=#gggg');
  $x['scheme']   => 'http'
  $x['host']     => 'example.com'
  $x['path']     => '/myfolder/sympony.mp3'
  $x['query']    => 'aa=1&bb=2?cc='
  $x['fragment'] => 'gggg'

 PATHINFO documentation

$x =  pathinfo('http://example.com/myfolder/sympony.mp3?aa=1&bb=2?cc=#gggg');
  $x['dirname']     => 'http://example.com/myfolder'
  $x['basename']    => 'sympony.mp3?aa=1&bb=2?cc=#gggg'
  $x['extension']   => 'mp3?aa=1&bb=2?cc=#gggg'
  $x['filename']    => 'sympony'