On my xpage I have an xp:messages for which I have adapted the UI to Boostrap/corporate standard.
Therefor I have placed the control inside a xp:panel control.
I wonder how I could compute the rendered property of this panel based upon if the xp:messages control has any items in it or not. I could not find an answer on SO.
If you display inside the message component an error, you can check the FacesContext.getMessage()
For more details see the answer, Get error messages