Major Description
If there is no render kit configured via WEB-INF/faces-config.xml, ServletContext init param or META-INF/faces-config.xml then JSF implementation must check META-INF/services directory for a file with a filename equal to the name of the factory.
From page 10-6 of the spec:
If a META-INF/services/
{factory-class-name}resource is visible to the web application class loader for the calling application (typically as a result of being present in the manifest of a JAR file), its first line is read and assumed to be the name of the factory implementation class to use.