Site shortage: nested includes.

Hello everyone, I've been over the "include" sections of this site, and found a woefully overlooked details: the nesting of include. php's include is a great asset of the php facility, but there is very little treatment of its ability to nest. Also known --- incorrectly --- as recursion. So tell me, what is php's ability to nest its include statements. By experience, I've found that it is only one deep. An include that has a further include does NOT get additional includes processed. I haven't found a specific explanation of this specific expectation anywhere. I hope to find it now. Thanks in advance, I love php! David Weeks