Introducing Quercus, a Java-based PHP framework

Quercus is a new approach to authoring Web services and applications using a mixture of Java™ technology and PHP. With the Quercus framework, Java and PHP are integrated with each other, thus allowing you to conveniently incorporate versatile Java libraries like Spring and Hibernate into applications.

Read the full article on the IBM website.

While I am finding out what I can about Quercus it seems to be the PHP engine driving PHP in Liferay.
It seems to be held in the JAR files quercus.jar, resin-util.jar, and javamail-141.jar.

The php.ini file is used to configure the PHP behavior, like setting directories, file paths, changing sessions, and so on. This file can be specified in the web.xml file.
SOme thing like this:

<init-param>
 <param-name>ini-file</param-name>
       <param-value>WEB-INF/php.ini</param-value>
</init-param>

If this is associated with the QuercusServlet, I do not know.