diff --git a/vendor/github.com/xdg/stringprep/set.go b/vendor/github.com/xdg/stringprep/set.go
new file mode 100644
index 0000000..c837e28
--- /dev/null
+++ b/vendor/github.com/xdg/stringprep/set.go
@@ -0,0 +1,36 @@
+// Copyright 2018 by David A. Golden. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License. You may obtain
+// a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
+
+package stringprep
+
+import "sort"
+
+// RuneRange represents a close-ended range of runes: [N,M].  For a range
+// consisting of a single rune, N and M will be equal.
+type RuneRange [2]rune
+
+// Contains returns true if a rune is within the bounds of the RuneRange.
+func (rr RuneRange) Contains(r rune) bool {
+	return rr[0] <= r && r <= rr[1]
+}
+
+func (rr RuneRange) isAbove(r rune) bool {
+	return r <= rr[0]
+}
+
+// Set represents a stringprep data table used to identify runes of a
+// particular type.
+type Set []RuneRange
+
+// Contains returns true if a rune is within any of the RuneRanges in the
+// Set.
+func (s Set) Contains(r rune) bool {
+	i := sort.Search(len(s), func(i int) bool { return s[i].Contains(r) || s[i].isAbove(r) })
+	if i < len(s) && s[i].Contains(r) {
+		return true
+	}
+	return false
+}