PHP offers great wrapper for fast libevent API. Extension code can be obtained from project repository and prebuild extensions, including DLLs for Windows, are available via PECL.
Modern IDEs are using something called "stubs" in order to provide accurate code
completion and many more advanced features while working with code. Stubs in their nature
are valid PHP files containing only classes/methods/functions/constants/etc declarations.
While PHP lacks header files (e.g. *.h used in C), stubs contents is virtually the same.
This repository contains such header files generic for any PHP IDE in order to provide
advanced coding features for Event library.
Refer to your IDE manual. The simplest thing, which should work in most IDEs, is downloading stubs to a directory and adding such folder to an include path.