How to add custom data into OOXML for powerpoint?

Question

I have a PPD document in which I need to append some custom XML data for reference. My xml data is like this

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>

<c:chartSpace xmlns:c="http://schemas.openxmlformats.org/drawingml/2006/chart"
xmlns:a="http://schemas.openxmlformats.org/drawingml/2006/main"
xmlns:r="http://schemas.openxmlformats.org/officeDocument/2006/relationships"
xmlns:c16r2="http://schemas.microsoft.com/office/drawing/2015/06/chart">

<c:date1904 val="0"/>

   other data...

</c:chartSpace>

I was trying to add metadata like this

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>

<c:chartSpace xmlns:c="http://schemas.openxmlformats.org/drawingml/2006/chart"
xmlns:a="http://schemas.openxmlformats.org/drawingml/2006/main"
xmlns:r="http://schemas.openxmlformats.org/officeDocument/2006/relationships"
xmlns:c16r2="http://schemas.microsoft.com/office/drawing/2015/06/chart">

<c:date1904 val="0"/>

<c:authorMeta>
    <c:authorId>23</c:authorId>
    <c:authorName>User 1</c:authorName>
</c:authorMeta>

   other data...

</c:chartSpace>

But looks like PowerPoint remove those contents from the presentation. Am I missing anything? What is the correct way to resolve this issue?

Update:

There is an open-source library called pptgenjs used to create pptx files. Which creating the chart the library concatenates the XML tags and creates a chart.xml file. While doing this thing I was trying to add some custom meta passed by the user. But while opening this in Powerpoint the tags are automatically removed. That's why I asked if there any specific specs to add custom tags in pptx XML files.

How the custom XML added?

I was using the PptxGenJs library to create the presentation. In that library, I edited the makeXmlCharts function and added my custom XML data into it.

   function makeXmlCharts(rel) {
      var strXml = '<?xml version="1.0" encoding="UTF-8" standalone="yes"?>';
      // other code
      strXml += '<customTag>data</customTag>'
      // other code

      return strXml;
   }

And finallay using the ppt.write('base64') to get the base64 data.

pptx.write('base64').then(async function(data) {
  await PowerPoint.run(async function(context) {
    context.presentation.insertSlidesFromBase64(data);
    await context.sync();
  });
}).catch(err=> {
  console.log(err)
})

This is how I insert the edited XML data into the PPTX file.