Simplify Change Tracking Data Model

It seems to me the new model for change tracking is too complicated to be implemented without a) a lot of efforts and b) mistakes.
Having different types of content in <item> and <simpleItem> based on the property attribute and the grand-parent element's
appliesTo attribute is not going to make things easy.

I would propose to simplify things:

If the change is on the content of a <source> or <target>:
-> Use a <contentItem> element that contains text and zero or more inline codes (same as a source or target content)

If the change is on the content of a <unit> (e.g. segmentation):
-> Use a <unitItem> element that contains one or more <segment> and zero or more <ignorable> (same as in <unit>)

In all other cases:
-> Use an <item> element that has plain text

• Neither <contentItem> nor <unitItem> would have a property attribute, or if they do it would be default and fixed to 'content'.
• The property in <item> could be set to 'content' only if the revisions' appliesTo is 'note'

As for dealing with orphan <sm/> and <em> in <contentItem>: I would propose to make them <mrk> with a new CTR attribute
ctr:added='sm|em' to indicate that the original was either a <em/> (added='em')or a <sm/> (added='sm').