I set up in "Eclipse Preferences->JBossTools->Web->JSF->Project->JSF Environment" JSF 2.3. When opening any facelets xhtml page in "JBoss Tools Html Editor" and putting a tag, for example:

<ui:fragment rendered="true"/>

then I accept that the property "rendered" is shown in the code completion. However, it is not, so it seems that JBoss Tools does not add the "JSF Environment 2.3" to my project.

_By the way, for the "rendered"-property, it was a bug in the "JSF 2.0 facelets tag declaration" which was fixed in 2.1 (https://stackoverflow.com/questions/3713468/alternative-to-uifragment-in-jsf)._

Anyway, if I set up "JSF Environment" to "JSF 2.3", then it would be nice to also use the "JSF 2.3 tag declarations" to the whole project environment.