I've noticed that different versions of php are located in different
directories (pkgsrc tree updated on 17/11/05)

lang/php
lang/php5
www/php4

This is a bit confusing...

What's the difference between lang/php and lang/php5?

ftp://ftp.netbsd.org/pub/NetBSD/packages/pkgsrc/lang/README.html contains a
list of packages in that directory, which does not include any php packages.
Why?