Most languages have one or more published standards. Here are some useful links:
If I'm honest, I find PHP a pretty ugly language. For me, it falls into the category of "a programming language designed by someone who had no business designing a programming language." Oops, did I just say that out loud? Anyway, anything that can help improve it has to be a good thing.
Both of these standards are published by the PHP Framework Interop Group:
This is the bit intended to ensure interoperability between shared PHP code.
Extending the previous guide, this describes recommended formatting options.
My favourite language, as I like to tell people at every opportunity. Although this is mainly considered a language for academics, there are still published code standards.
Actually, most of the published standards are derived from this one published paper. Given that the list of authors reads like a brief who's who of Prolog development, that's probably fair enough.
Published by Sylvain Soliman, this guide strays off into non-standards based discussion toward the end. However, most of it is decent.