One great feature about IDEs is autocomplete depending on the context. Of course there is a lot of suggestions when it comes to JSF tags based on the namespace but there is also suggestions inside JSF attributes depending on several factors and on the IDE.
RichFaces CDK has a "suggested-value" inside the @Attribute annotation which map the "suggested-value" of the faces-config.xml file (see http://horstmann.com/corejsf/faces-config.html#suggested-value ) which purpose should be to help IDEs. But so far, it isn't working so nicely...
Since I'm using Eclipse + JBoss Tools, that's were I've starting to look. It appears that JBoos Tools do parse the faces-config.xml file but mostly for component and facet names, ignoring the "suggested-value".
The process of JBoss Tools is described here: https://community.jboss.org/wiki/NewKBPlug-inAndCodeAssistInJBossTools310M3 . So, in fact, it parse taglibs and faces-config.xml files but fallback to hard coded files when it can't find any suggestion (they are located here: https://github.com/jbosstools/jbosstools-jst/tree/master/plugins/org.jboss.tools.jst.web.kb/taglibs ).
I've created a JBoss Tools issue in order to check the suggested-value property when present: https://issues.jboss.org/browse/JBIDE-13237
I couldn't find any real documentation about IntelliJ Idea autocomplete. Maybe Brian can tell us a bit more about that when he is using it. I will search about NetBeans later.