XSpec support Phase 2: refinements, extensions and testing

[wendellpiez]

Committer Notes

This PR should complete work initiated with #5, at least relative to the goal of 'stable and well documented' XSpec support of XSLT.

NB - Schematron and XQuery are for the moment Nice To Have, not blocking requirements.

All Submissions:

• Follow Contributing guidelines
• Make no changes duplicating or conflicting with other open Pull Requests
• Have been squashed to keep only relevant interim commits, if any [instructions]
• Have been tested manually
• Pass all CI/CD checks

Changes to Core Features:

• The Issue history, discussions and new documentation provide context for new features -- everything is reasonably self-explanatory
• New tests are included
• New examples are included
• Everything in readme and TESTING documents has been updated

[github-actions]

XSpec Test Results

0 tests  ±0   0 ✅ ±0   0s ⏱️ ±0s
0 suites ±0   0 💤 ±0 
0 files   ±0   0 ❌ ±0 

Results for commit b4e40bb. ± Comparison against base commit 214e349.

♻️ This comment has been updated with latest results.