Interface changes: none.
- Improvement (a11y): add titles and ARIA labels to elements (via #4130, 4127)
- Bugfix (rendering): improve spacing and punctuation in parameter enum display (via #4144)
- Bugfix (rendering): right-align tag expand/collapse button, even when the tag has no description (via #4129)
- Bugfix (try-it-out): surface parameter validation error messages to OAS3 users (via #4162)