Committer Notes

This PR provides significant support for additional HTML tags in the markup-line and markup-multiline implementations.

Support is added for:

• <hr/>
• <blockquote>
• <br>
• <code class="someclass">

Titles are now allowed on <a title="sometitle"> and <img title="sometitle"/> tags. This was a major oversight.

List items (<li>) are now more robust in the content they allow. They now allow <pre>, <hr/>, and <blockquote>, headings, and <p> tags.

These schema changes support usnistgov/metaschema-xslt#9, usnistgov/metaschema-xslt#16, and usnistgov/metaschema-xslt#21.

All Submissions:

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you squashed any non-relevant commits and commit messages? [instructions]
• Do all automated CI/CD checks pass?

Changes to Core Features:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your core changes, as applicable?
• Have you included examples of how to use your new feature(s)?
• Have you updated all website](https://pages.nist.gov/metaschema) and readme documentation affected by the changes you made? Changes to the website can be made in the website/content directory of your branch.