If you create an element with the inputValueCalc property expressed like this

<xs:element name="value">

<xs:annotation><xs:appinfo source="http://www.ogf.org/dfdl/">

    <dfdl:property name="inputValueCalc"><![CDATA[

      { ...expression }

    ]]></dfdl:property>

</xs:appinfo></xs:annotation>

<xs:simpleType>

...

</xs:simpleType>

</xs:element>

At compilation time this will not cause an error, even though a dfdl:element annotation is required, and dfdl:property is not allowed like this. (BUG 1)
So silently, this asks for length property to be defined, because it isn't seeing this as an
IVC at all.