code: func PackageMatches(pkg *vpython.Spec_Package, tags []*vpython.PEP425Tag) bool {
  	// If any "not_match_tag" matches, then this package does not match.
  	for _, matchTag := range pkg.NotMatchTag {
  		if PEP425Matches(matchTag, tags) {
  			return false
  		}
  	}
  
  	// If we have no match tags, or if a match tag matches a host tag, then the
  	// package matches.
  	if len(pkg.MatchTag) == 0 {
  		return true
  	}
  	for _, matchTag := range pkg.MatchTag {
  		if PEP425Matches(matchTag, tags) {
  			return true
  		}
  	}
  	return false
  }
docs: // PackageMatches returns true if the package's match constraints are compatible
  // with tags. A package matches if:
  //
  //	- None of the tags matches any of the "not_match_tag" entries, and
  //	- Every "match_tag" entry matches at least one tag.
  //
  // As a special case, if the package doesn't specify any match tags, it will
  // always match regardless of the supplied PEP425 tags. This handles the deafult
  // case where the user specifies no constraints.
  //
  // See PEP425Matches for information about how tags are matched.