Google isn't the best place to look for object/method references. I've worked with a lot of large PHP codebases and the answer is always in the local source files or, if they're too obtuse, then on the project's documentation (if it exists and is current), in the PHP manual, or in a Google search result.

Any editor worth its salt can manipulate a cross-reference of the project's symbols. Learning how to do this has saved me days of time figuring out OO-heavy projects. I prefer ctags(1) and Vim.