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"... Every Java EE application server comes with a bundled JSF implementation. Often the reference implementation (RI), known as "Mojarra", is used for this. However, you can bundle an alternative JSF implementation to be used with your project. This way, you can use MyFaces Core as JSF implementation on every Java EE application server. One of the benefits of using MyFaces Core is that it generates more informative logging, which can be helpful while debugging. If you're looking for an application server that uses MyFaces Core by default, you should take a look at Apache Geronimo..." Thanks to Bart Kummel for provide this text from its book Apache MyFaces 1.2 Web Application Development
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