Links to External Sites in PHP
In real life, a website can have a mix of absolute paths, relative paths, and paths to external sites. We need to be able to filter out links leading to external sites.
Let targ.loc be the site
that we are parsing.
Get an array of href leading
to this site, perform their normalization,
excluding links to external sites:
<a href="page.html">text</a>
<a href="./page.html">text</a>
<a href="../page.html">text</a>
<a href="http://targ.loc/page.html">text</a>
<a href="https://targ.loc/page.html">text</a>
<a href="http://othr.com/dir/page.html">text</a>
<a href="https://othr.com/dir/page.html">text</a>
