<https://secure.gravatar.com/avatar/af5fc5dd830812b927e0fac3c2c0844d?s=96&amp;d=wavatar&amp;r=g>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://tuhocict.com/kieu-chuoi-ky-tu-string-trong-php/>