New DTD for Meta Tag Markup Language

I want to introduce my concept for a new DTD that serves as an XML-based
markup language called Meta Tag Markup Language (or "MTML"). The basic
premise is to use HTML-based SEO meta tags schema in an
XML file/environment. I am hoping this could help reduce the workload and
file size of HTML and/or other index pages.

This is the basic mtml.dtd schema:

<!DOCTYPE document [
  <!ELEMENT document (title, description, robots, author?, copyright?,
viewport?, keywords?)>
  <!ELEMENT title (#PCDATA)>
  <!ELEMENT description (#PCDATA)>
  <!ELEMENT robots (#PCDATA)>
  <!ELEMENT author (#PCDATA)>
  <!ELEMENT copyright (#PCDATA)>
  <!ELEMENT viewport (#PCDATA)>
  <!ELEMENT keywords (#PCDATA)>
]>

And this is an example of a placeholder file called meta-tags.xml (can be
renamed if you wish):

<?xml version="1.0" encoding="UTF-8"?>
<document>
  <title>This is the title of the page</title>
  <description>This is a brief description of the page</description>
  <robots>index</robots>
  <author>This is the name of the author</author>
  <copyright>This is the name of the copyright holder</copyright>
  <viewport content="width=device-width, initial-scale=1.0" />
  <keywords>This is a list of keywords for the page</keywords>
</document>

May I get some thoughts on the effectiveness of such a markup language and
whether or not it would improve SEO efforts? Any way to make MTML better?

The license given to MTML is CC0 1.0 Universal and documentation can be
found here:

https://archive.org/details/meta-tag-markup-language

Best regards,

Joseph D. Smith🥷