Parse parses a constraint string using a syntax similar to that used by npm, Go "dep", Rust's "cargo", etc.

ParseExactVersion parses a string that must contain the specification of a single, exact version, and then returns it as a VersionSpec.

ParseRubyStyle parses a single selection constraint using a syntax similar to that used by rubygems and other Ruby tools.

ParseRubyStyleAll is a helper wrapper around ParseRubyStyle that accepts multiple selection strings and combines them together into a single IntersectionSpec.

ParseRubyStyleMulti is similar to ParseRubyStyle, but rather than parsing only a single selection specification it instead expects one or more comma-separated specifications, returning the result as an IntersectionSpec.

SelectionSpec represents applying a single operator to a particular "boundary" version.

VersionSpec represents the boundary within a SelectionSpec.

Spec is an interface type that UnionSpec, IntersectionSpec, SelectionSpec, and VersionSpec all belong to.

IntersectionSpec represents an "and" operation on nested version constraints.

UnionSpec represents an "or" operation on nested version constraints.