el expression in zk .

Some EL characters are illegal in XML attribute or ZK annotation, you should replace them with other EL operators. 

Character	Replacement
=	eq
!=	ne
&&	and
<	lt
<=	le
>	gt
>=	ge


For example:

<label value="@bind(vm.age lt 18?'true':'false')"/>
<image src="@load(vm.picture ne null ? 'images/'.concat(vm.picture) : 'images/NoImage.png')"/>