Not Mandatory. Some property bindings must be read-write. For example, if you bind the value of a component that implements [EditableValueHolder](http://java.sun.com/javaee/6/docs/api/javax/faces/component/EditableValueHolder.html). Other properties can be read-only. If you use the binding attribute for dynamically creating component instances, this must also be read-write as per the contract defined in the specification.