If you work with Markdown documents (.md files) or SVG images, you may find these new viewers useful.
Microsoft have updated their PowerToys for Windows 10 with viewers for both formats.
Details, links and screenshots of what they look like within Directory Opus can be found here:
For Markdown, there is also a second, alternative viewer linked at the bottom of the post, in case it works better for you.
For SVG, you can also preview .SVG files via Internet Explorer's built-in support, which Opus will use by default in the viewer pane if nothing else is installed.