Seeking an example that illustrates the need for dfdl:contentLength

[Roger L Costello]

Hi Folks,

My (binary) input file consists of:

  *   Two bytes (little endian) indicating the length of the following person 
data
  *   Person info, consisting of:
     *   Person name, null terminated
     *   Person digital identifier, 20 hex digits

At the end of this message is my DFDL schema. It parses the input fine. Parsing 
generates this XML:

<SimpleDataFormat>
  <length>29</length>
  <personInfo>
    <name>John Doe</name>
    <digital-id>AE6E4D1209F17B460503904FAD297B31E9CF6362</digital-id>
  </personInfo>
</SimpleDataFormat>

It also unparses fine.

There was no need to use contentLength. How can I modify/add-to the example so 
that contentLength must be used to properly unparse? I want the example to 
require this:

<xs:element name="length" type="xs:nonNegativeInteger"
    dfdl:lengthKind="explicit"
    dfdl:length="2"
    dfdl:lengthUnits="bytes"
    dfdl:outputValueCalc='{ dfdl:contentLength(../personInfo) }'
/>
<xs:element name="personInfo"
    dfdl:lengthKind="explicit"
    dfdl:length="{../length}"
    >
    ...
</xs:element>

Here is my current DFDL schema:

<xs:element name="SimpleDataFormat"
    dfdl:lengthKind="implicit"
    >
    <xs:complexType>
        <xs:sequence>
            <xs:element name="length" type="xs:nonNegativeInteger"
                dfdl:lengthKind="explicit"
                dfdl:length="2"
                dfdl:lengthUnits="bytes"
            />
            <xs:element name="personInfo"
                dfdl:lengthKind="explicit"
                dfdl:length="{../length}"
                >
                <xs:complexType>
                    <xs:sequence>
                        <xs:element name="name" type="xs:string"
                            dfdl:encoding="ASCII"
                            dfdl:terminator="%NUL;"
                            dfdl:emptyValueDelimiterPolicy="terminator"
                            dfdl:lengthKind="delimited"
                        />
                        <xs:element name="digital-id" type="xs:hexBinary"
                            dfdl:lengthKind="explicit"
                            dfdl:length="20"
                            dfdl:lengthUnits="bytes"
                        />
                    </xs:sequence>
                </xs:complexType>
            </xs:element>
        </xs:sequence>
    </xs:complexType>
</xs:element>