Only valid elements should be inserted about oxygen-dita-prolog-updater-addon

[raducoravu]

Thanks, we'll look into this as well.

[DunaMariusCosmin]

Hi @xephon2,
What do you think if the document will be update like this:

<?xml version="1.0" encoding="UTF-8"?>
<?xml-model href="urn:oasis:names:tc:dita:spec:classification:rng:subjectScheme.rng" schematypens="http://relaxng.org/ns/structure/1.0"?> 
<subjectScheme>
    <topicmeta>
        <author type="contributor">Stefan.Eike</author> 
        <critdates> 
            <!--Stefan.Eike-->
            <revised modified="2018/02/14"/>
        </critdates>
    </topicmeta>
    <subjectHead>
        <subjectHeadMeta>
            <navtitle>
                <!-- Enter a description of the subject scheme. -->
            </navtitle>
        </subjectHeadMeta>
    </subjectHead>
    
    <!-- ... -->
</subjectScheme>

It's ok for you to add the prolog information(author and critdates) in topicmeta element?