code: func verifySelectiveFlags(flags, establishedFlags uint32) (valid bool, missing, extra uint32) {
  	missing = flags&establishedFlags ^ flags
  	extra = flags | establishedFlags ^ flags
  	valid = missing == 0
  	return valid, missing, extra
  }
docs: // verifySelectiveFlags determines if all bits requested in flags are set in establishedFlags.
  // missing represents the bits set in flags that are not set in establishedFlags.
  // extra represents the bits set in establishedFlags that are not set in flags.
  // valid is true and missing is zero when establishedFlags has all of the requested flags.