new files. **Do not add RELNOTE=yes comments in CLs.** Instead, add a file to
the CL (or ask the author to do so).

At the end of the development cycle, the files will be merged by being
concatenated in sorted order by pathname. Files in the directory matching the
glob "*stdlib/*minor" are treated specially. They should be in subdirectories
corresponding to standard library package paths, and headings for those package

// The key must not contain an '=' character.
func validPAXRecord(k, v string) bool {
	if k == "" || strings.Contains(k, "=") {
		return false
	}
	switch k {
	case paxPath, paxLinkpath, paxUname, paxGname:
		return !hasNUL(v)
	default:
		return !hasNUL(k)
	}