How to extend an sdlxliff without the "The xxxx element is not declared" error?

Question

Hello, 
 I am looking to add my custom xml elements inside a sdlxliff per this section at the extension point right under the <xliff> element . However, when I open an xliff that has my own custom-namespace XML tags in Studio, it complains and gives an error like "The xxxx element is not declared". I know I can disable the schema validation in the SDLXLIFF filetype settings, but I don't want all of my clients to go through this setting adaptation. Is there a way to properly declare custom XML elements without Trados complaining? 
 Thanks

Paul · Answer

Stelios Mathioulakis 
 Perhaps you can explain what you are trying to achieve? I confirmed with Patrick Andrew Hartnett that we have manipulated SDLXLIFF in our appstore projects before to support unusual workflows, but always by using the FileTypeSupport.Framework to read and write the SDLXLIFF files. 
 We persist meta-data, such as the back-translation with the TranslationOrigin in our Trados Transcreate application. We included this to facilitate automation in the workflow as there are detached procedures in the workflow . 
 If this is the sort of thing that would help then search for "back-translation" in the source code of this project: 
 https://github.com/RWS/Sdl-Community/tree/master/SDLTranscreate

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How to extend an sdlxliff without the "The xxxx element is not declared" error?