On the "24 Days in December" advent calendar there's an article posted from Kalle Sommer Nielsen that talks about some ways that you can give back to PHP including documentation updates, contributing to the core code and just helping out the community in general.

PHP has a tremendous community behind it, that community consists of you and me, and millions of others that help promote PHP by continuing to develop awesome applications that power some of the biggest websites in the world, but within this community exists a relatively small community that actively develops PHP, such as making it run on your favorite platform or making your favorite extensions compile and work or even keeps the documentation up-to-date. Today I want to dwell into that community, and perhaps giving you flavor enough to contribute back to PHP with code.

The article suggests several places you can give back including:

• updating and adding changes to the PHP manual documentation
• participating in the various project mailing lists
• reviewing pull requests on the project's GitHub repository
• writing tests for the untested parts of the language

Kalle wraps up the article talking about his own experience with the language over the years and how it ended up that he was the one to remove register_globals from the language one day.