No public documentation on why "--classic" is required (or desired)

[Joshfindit]

Pages that came up through an initial Google search for answers:

• https://www.ruby-lang.org/en/news/2018/11/08/snap/
• https://snapcraft.io/ruby
• https://snapcraft.io/install/ruby/ubuntu
• https://www.ruby-lang.org/en/downloads/ (this site doesn't even mention snap "Ways of Installing Ruby" section)

[nottrobin]

I'm trying to use Ruby inside a snap, but my snap is strictly confined. I'd love to understand which pieces of Ruby require it to be run in --classic confinement so I can tell whether achieving this is possible or impossible.