This is just a first draft, and I'm sure there's still a lot of explanatory prose that could be really helpful. Some open questions:

• @steveklabnik Does this reflect what the semver crate is doing with range parsing?
• Other implementors: how far is this spec from what you're doing with semver ranges? Would it be onerous or disruptive to implement in this way? Does anything conflict with your system's behavior today, or are there other features you've implemented that should go in this spec, so we can drive to consistency? (I seem to recall that ~ in particular is subtly different between rubygems/bundler and npm?)
• Does this belong in semver.org, or should it be its own standalone thing, like semver-ranges.org or something? (I'd definitely like it to be owned by this group, whether it's on this specific domain name or another one.)
• What questions does it raise for you that you'd like answered? What questions do you expect from others in your communities?