Indeed, I've reached the same conclusion about the detection of the EL
I don't think we're actually using expressions explicitly, but I think we use @Max, which seems to be similar to @DecimalMax.
At runtime we use Tomcat 8.0, which I think provides an implementation through jasper-el.
And now I see that there was another module which had a test dependency on org.glassfish:javax.el, but not this one.

Thanks for the help