diff --git a/lib/zlibcut/example_test.go b/lib/zlibcut/example_test.go
new file mode 100644
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+++ b/lib/zlibcut/example_test.go
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+// Copyright 2019 The Wuffs Authors.
+//
+// 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
+//
+//    https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package zlibcut_test
+
+import (
+	"bytes"
+	"compress/zlib"
+	"fmt"
+	"io/ioutil"
+	"strings"
+
+	"github.com/google/wuffs/lib/zlibcut"
+)
+
+func ExampleCut() {
+	const sonnet18 = "" +
+		"Shall I compare thee to a summer’s day?\n" +
+		"Thou art more lovely and more temperate.\n" +
+		"Rough winds do shake the darling buds of May,\n" +
+		"And summer’s lease hath all too short a date.\n" +
+		"Sometime too hot the eye of heaven shines,\n" +
+		"And often is his gold complexion dimmed;\n" +
+		"And every fair from fair sometime declines,\n" +
+		"By chance, or nature’s changing course, untrimmed;\n" +
+		"But thy eternal summer shall not fade,\n" +
+		"Nor lose possession of that fair thou ow’st,\n" +
+		"Nor shall death brag thou wand'rest in his shade,\n" +
+		"When in eternal lines to Time thou grow'st.\n" +
+		"So long as men can breathe, or eyes can see,\n" +
+		"So long lives this, and this gives life to thee.\n"
+
+	if n := len(sonnet18); n != 632 {
+		fmt.Printf("len(sonnet18): got %d, want 632", n)
+		return
+	}
+
+	// Compress the input text, sonnet18.
+	buffer := &bytes.Buffer{}
+	w := zlib.NewWriter(buffer)
+	w.Write([]byte(sonnet18))
+	w.Close()
+	compressed := buffer.Bytes()
+
+	// The exact length of the zlib-compressed form of sonnet18 depends on the
+	// compression algorithm used, which can change from version to version of
+	// the Go standard library. Nonetheless, for a 632 byte input, we expect
+	// the compressed form to be between 300 and 500 bytes.
+	if n := len(compressed); (n < 300) || (500 < n) {
+		fmt.Printf("len(compressed): got %d, want something in [300, 500]", n)
+		return
+	}
+
+	// Cut the 300-or-more bytes to be 200.
+	encodedLen, decodedLen, err := zlibcut.Cut(nil, compressed, 200)
+	if err != nil {
+		fmt.Printf("Cut: %v", err)
+		return
+	}
+
+	// The encodedLen should be equal to or just under the requested 200.
+	cut := compressed[:encodedLen]
+	if n := len(cut); (n < 190) || (200 < n) {
+		fmt.Printf("len(cut): got %d, want something in [190, 200]", n)
+		return
+	}
+
+	// At this point, a real program would write that cut slice somewhere. The
+	// rest of this example verifies that the cut data has the properties we
+	// expect, given the semantics of zlibcut.Cut.
+
+	// Uncompress the cut data. It should be a valid zlib-compressed stream, so
+	// no errors should be encountered.
+	r, err := zlib.NewReader(bytes.NewReader(cut))
+	if err != nil {
+		fmt.Printf("NewReader: %v", err)
+		return
+	}
+	uncompressed, err := ioutil.ReadAll(r)
+	if err != nil {
+		fmt.Printf("ReadAll: %v", err)
+		return
+	}
+	err = r.Close()
+	if err != nil {
+		fmt.Printf("Close: %v", err)
+		return
+	}
+
+	// The uncompressed form of the cut data should be a prefix (of length
+	// decodedLen) of the original input, sonnet18. Again, the exact length
+	// depends on the zlib compression algorithm, but uncompressing 200 or so
+	// bytes should give between 250 and 400 bytes.
+	if n := len(uncompressed); n != decodedLen {
+		fmt.Printf("len(uncompressed): got %d, want %d", n, decodedLen)
+		return
+	} else if (n < 250) || (400 < n) {
+		fmt.Printf("len(uncompressed): got %d, want something in [250, 400]", n)
+		return
+	} else if !strings.HasPrefix(sonnet18, string(uncompressed)) {
+		fmt.Printf("uncompressed was not a prefix of the original input")
+		return
+	}
+
+	// The first two lines of the sonnet take 83 bytes.
+	fmt.Println(string(uncompressed[:83]))
+	// Output:
+	// Shall I compare thee to a summer’s day?
+	// Thou art more lovely and more temperate.
+}