What is the complaint and type of the marker?
I believe it's the Facelet Validator (Eclipe WTP). See https://bugs.eclipse.org/bugs/show_bug.cgi?id=352491
Should be fixed in WTP 3.3.1.
JBT works fine with such an EL syntax.
You can disable Facelet Validator in Window->Preferences->Validation->Facelet HTML Validator or update your Eclipse WTP to the latest 3.3.1
That update resolved it, thanks Alexey.