If you don't already know how to implement them you aren't supposed to implement them. The spec even tells you not to implement them (and Microsoft does not implement them). They are there for third parties who reverse engineered ancient Word and WordPerfect formats and built tool chains around them, and want to move to a newer format but need to mark places where they depend on quirks of those ancient programs.
Here's the use case this is aimed at. Suppose I run, say, a law office, and we've got an internal document management system that does things like index and cross reference documents, manage citation lists, and stuff like that. The workflow is based on WordPerfect format (WordPerfect was for a long time the de facto standard for lawyers).
Now suppose I want to start moving to a newer format for storage. Say I pick ODF, and start using that for new documents, and make my tools understand it. I'd like to convert my existing WordPerfect documents to ODF. However, there are things in WordPerfect that cannot be reproduced exactly in ODF, and this is a problem. If my tools need to figure out what page something is on, in order to generate a proper citation to that thing, and I've lost some formatting information converting to ODF, I may not get the right cite.
So what am I going to do? I'm going to add some extra, proprietary markup of my own to ODF that lets me include my reverse engineered WordPerfect knowledge when I convert my old documents to ODF, and my new tools will be modified to understand this. Now my ODF workflow can generate correct cites for old documents. Note that LibreOffice won't understand my additional markup, and will presumably lose it if I edit a document, but that's OK. The old documents I converted should be read-only.
Of course, I'm not the only person doing this. Suppose you also run a law office, with a WordPerfect work flow, and are converting to an ODF work flow. You are likely going to add some proprietary markup, just like I did. We'll both end up embedding the same WordPerfect information in our converted legacy documents, but we'll probably pick different markup for it. It would be nice if we could get together, make a list of things we've reverse engineered, and agree to use the same markup when embedding that stuff in ODF.
And that's essentially what they did in OOXML. They realized there would be people like us with our law offices, who have reverse engineered legacy data, that will be extending the markup. So they made a list of a bunch of things from assorted past proprietary programs that were likely to have been reverse engineered by various third parties, and reserved some markup for each.
Here's the use case this is aimed at. Suppose I run, say, a law office, and we've got an internal document management system that does things like index and cross reference documents, manage citation lists, and stuff like that. The workflow is based on WordPerfect format (WordPerfect was for a long time the de facto standard for lawyers).
Now suppose I want to start moving to a newer format for storage. Say I pick ODF, and start using that for new documents, and make my tools understand it. I'd like to convert my existing WordPerfect documents to ODF. However, there are things in WordPerfect that cannot be reproduced exactly in ODF, and this is a problem. If my tools need to figure out what page something is on, in order to generate a proper citation to that thing, and I've lost some formatting information converting to ODF, I may not get the right cite.
So what am I going to do? I'm going to add some extra, proprietary markup of my own to ODF that lets me include my reverse engineered WordPerfect knowledge when I convert my old documents to ODF, and my new tools will be modified to understand this. Now my ODF workflow can generate correct cites for old documents. Note that LibreOffice won't understand my additional markup, and will presumably lose it if I edit a document, but that's OK. The old documents I converted should be read-only.
Of course, I'm not the only person doing this. Suppose you also run a law office, with a WordPerfect work flow, and are converting to an ODF work flow. You are likely going to add some proprietary markup, just like I did. We'll both end up embedding the same WordPerfect information in our converted legacy documents, but we'll probably pick different markup for it. It would be nice if we could get together, make a list of things we've reverse engineered, and agree to use the same markup when embedding that stuff in ODF.
And that's essentially what they did in OOXML. They realized there would be people like us with our law offices, who have reverse engineered legacy data, that will be extending the markup. So they made a list of a bunch of things from assorted past proprietary programs that were likely to have been reverse engineered by various third parties, and reserved some markup for each.