Coding conventions are a set of guidelines for a specific programming language that recommend programming style, practices and methods for each aspect of a piece program written in this language. These conventions usually cover file organization, indentation, comments, declarations, statements, white space, naming conventions, programming practices, programming etc
PHP Framework Interoperability Group (Link) is a group composed from representatives from top PHP open source projects to talk about the commonalities between our projects and find ways we can work together. their main audience is each other, but they are aware that the rest of the PHP community is watching and hopefully other folks like you reading this tip will adopt what they are doing in order to create better collaboration in the PHP community.
So far the group has confirmed 4 official standard documents:
PSR-0 - Autoloading standard
Describes the mandatory requirements that must be adhered to for autoloader interoperability.
PSR-1 - Basic coding standard
Comprises what should be considered the standard coding elements that are required to ensure a high level of technical interoperability between shared PHP code.
PSR-2 - Coding style guide
This guide extends and expands on PSR-1, the basic coding standard.
PSR-3 - Logger interface
This document describes a common interface for logging libraries.
Check out more @ http://www.php-fig.org/