• I believe this to be a bug, not a question about using Jekyll.
• I updated to the latest Jekyll (or) if on GitHub Pages to the latest github-pages
• I ran jekyll doctor to check my configuration
• I read the CONTRIBUTION file at https://jekyllrb.com/docs/contributing/
• This is a feature request.

• I am on (or have tested on) macOS 10+
• I am on (or have tested on) Debian/Ubuntu GNU/Linux
• I am on (or have tested on) Fedora GNU/Linux
• I am on (or have tested on) Arch GNU/Linux
• I am on (or have tested on) Other GNU/Linux
• I am on (or have tested on) Windows 10+

• I was trying to install.
• There is a broken Plugin API.
• I had an error on GitHub Pages, and I have reproduced it locally.
• I had an error on GitHub Pages, and GitHub Support said it was a Jekyll Bug.
• I had an error on GitHub Pages and I did not test it locally.
• I was trying to build.
• It was another bug.

My Reproduction Steps

{% include_relative file~path.html %}

The Output I Wanted

Currently include restricts file name/paths to A-Za-z0-9 + _-. only. This is unnecessarily restrictive. Instead, perhaps filter out known illegal characters, as opposed to whitelisting safe characters? e.g. error only if path contains: <>:"/\|?* (taking a broad cross-OS view of what counts as illegal).