When you visit any documentation page on php.net, your browser is redirected to a regional server, presumably to speed up response times.
For example, accessing php.net from the US, my browser is typically redirected to us.php.net, us2.php.net, etc.
Sounds great, except that links posted in questions and answers on SO retain those hostnames, so you end up seeing links to us.php.net, ru.php.net, be.php.net, de.php.net, etc.
This tends to defeat the purpose of having regionally-located servers if people are going to share links with people who live thousands of miles away from the servers that they point to.
It seems like this could be handled automatically and transparently via a regular expression search and replace, similar to automatic removal of salutations.
Note that there are a number of subdomains that should be left alone.
http://php.net/functionnamedoes the right thing. Linking to non-function-reference sections of the docs is a bit more challenging.