Please, can someone tell me how I can express
this constraint using Relax NG?
I want these documents to be valid:
<memo>
<code>WithMessage</code>
<message>WithMessage means there is a message.</message>
</memo>
<memo>
<code>WithoutMessage</code>
<!-- WithoutMessage so no message -->
</memo>
And these documents to be invalid:
<memo>
<code>WithoutMessage</code>
<message>This element shouldn't exist.</message>
</memo>
<memo>
<code>WithMessage</code>
<!-- There should be a message here -->
</memo>
Thanks.
James McComb