diff --git a/.travis.yml b/.travis.yml
index 588ceca..d4b9266 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,10 +1,14 @@
 language: go
 go_import_path: github.com/pkg/errors
 go:
-  - 1.4.3
-  - 1.5.4
-  - 1.6.2
-  - 1.7.1
+  - 1.4.x
+  - 1.5.x
+  - 1.6.x
+  - 1.7.x
+  - 1.8.x
+  - 1.9.x
+  - 1.10.x
+  - 1.11.x
   - tip
 
 script:
diff --git a/README.md b/README.md
index 273db3c..6483ba2 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,4 @@
-# errors [![Travis-CI](https://travis-ci.org/pkg/errors.svg)](https://travis-ci.org/pkg/errors) [![AppVeyor](https://ci.appveyor.com/api/projects/status/b98mptawhudj53ep/branch/master?svg=true)](https://ci.appveyor.com/project/davecheney/errors/branch/master) [![GoDoc](https://godoc.org/github.com/pkg/errors?status.svg)](http://godoc.org/github.com/pkg/errors) [![Report card](https://goreportcard.com/badge/github.com/pkg/errors)](https://goreportcard.com/report/github.com/pkg/errors)
+# errors [![Travis-CI](https://travis-ci.org/pkg/errors.svg)](https://travis-ci.org/pkg/errors) [![AppVeyor](https://ci.appveyor.com/api/projects/status/b98mptawhudj53ep/branch/master?svg=true)](https://ci.appveyor.com/project/davecheney/errors/branch/master) [![GoDoc](https://godoc.org/github.com/pkg/errors?status.svg)](http://godoc.org/github.com/pkg/errors) [![Report card](https://goreportcard.com/badge/github.com/pkg/errors)](https://goreportcard.com/report/github.com/pkg/errors) [![Sourcegraph](https://sourcegraph.com/github.com/pkg/errors/-/badge.svg)](https://sourcegraph.com/github.com/pkg/errors?badge)
 
 Package errors provides simple error handling primitives.
 
@@ -47,6 +47,6 @@ We welcome pull requests, bug fixes and issue reports. With that said, the bar f
 
 Before proposing a change, please discuss your change by raising an issue.
 
-## Licence
+## License
 
 BSD-2-Clause
diff --git a/bench_test.go b/bench_test.go
index 0416a3c..903b5f2 100644
--- a/bench_test.go
+++ b/bench_test.go
@@ -15,6 +15,7 @@ func noErrors(at, depth int) error {
 	}
 	return noErrors(at+1, depth)
 }
+
 func yesErrors(at, depth int) error {
 	if at >= depth {
 		return New("ye error")
@@ -22,8 +23,11 @@ func yesErrors(at, depth int) error {
 	return yesErrors(at+1, depth)
 }
 
+// GlobalE is an exported global to store the result of benchmark results,
+// preventing the compiler from optimising the benchmark functions away.
+var GlobalE error
+
 func BenchmarkErrors(b *testing.B) {
-	var toperr error
 	type run struct {
 		stack int
 		std   bool
@@ -53,7 +57,7 @@ func BenchmarkErrors(b *testing.B) {
 				err = f(0, r.stack)
 			}
 			b.StopTimer()
-			toperr = err
+			GlobalE = err
 		})
 	}
 }
diff --git a/errors.go b/errors.go
index 842ee80..7421f32 100644
--- a/errors.go
+++ b/errors.go
@@ -6,7 +6,7 @@
 //             return err
 //     }
 //
-// which applied recursively up the call stack results in error reports
+// which when applied recursively up the call stack results in error reports
 // without context or debugging information. The errors package allows
 // programmers to add context to the failure path in their code in a way
 // that does not destroy the original value of the error.
@@ -15,16 +15,17 @@
 //
 // The errors.Wrap function returns a new error that adds context to the
 // original error by recording a stack trace at the point Wrap is called,
-// and the supplied message. For example
+// together with the supplied message. For example
 //
 //     _, err := ioutil.ReadAll(r)
 //     if err != nil {
 //             return errors.Wrap(err, "read failed")
 //     }
 //
-// If additional control is required the errors.WithStack and errors.WithMessage
-// functions destructure errors.Wrap into its component operations of annotating
-// an error with a stack trace and an a message, respectively.
+// If additional control is required, the errors.WithStack and
+// errors.WithMessage functions destructure errors.Wrap into its component
+// operations: annotating an error with a stack trace and with a message,
+// respectively.
 //
 // Retrieving the cause of an error
 //
@@ -38,7 +39,7 @@
 //     }
 //
 // can be inspected by errors.Cause. errors.Cause will recursively retrieve
-// the topmost error which does not implement causer, which is assumed to be
+// the topmost error that does not implement causer, which is assumed to be
 // the original cause. For example:
 //
 //     switch err := errors.Cause(err).(type) {
@@ -48,16 +49,16 @@
 //             // unknown error
 //     }
 //
-// causer interface is not exported by this package, but is considered a part
-// of stable public API.
+// Although the causer interface is not exported by this package, it is
+// considered a part of its stable public interface.
 //
 // Formatted printing of errors
 //
 // All error values returned from this package implement fmt.Formatter and can
-// be formatted by the fmt package. The following verbs are supported
+// be formatted by the fmt package. The following verbs are supported:
 //
 //     %s    print the error. If the error has a Cause it will be
-//           printed recursively
+//           printed recursively.
 //     %v    see %s
 //     %+v   extended format. Each Frame of the error's StackTrace will
 //           be printed in detail.
@@ -65,13 +66,13 @@
 // Retrieving the stack trace of an error or wrapper
 //
 // New, Errorf, Wrap, and Wrapf record a stack trace at the point they are
-// invoked. This information can be retrieved with the following interface.
+// invoked. This information can be retrieved with the following interface:
 //
 //     type stackTracer interface {
 //             StackTrace() errors.StackTrace
 //     }
 //
-// Where errors.StackTrace is defined as
+// The returned errors.StackTrace type is defined as
 //
 //     type StackTrace []Frame
 //
@@ -85,8 +86,8 @@
 //             }
 //     }
 //
-// stackTracer interface is not exported by this package, but is considered a part
-// of stable public API.
+// Although the stackTracer interface is not exported by this package, it is
+// considered a part of its stable public interface.
 //
 // See the documentation for Frame.Format for more details.
 package errors
@@ -192,7 +193,7 @@ func Wrap(err error, message string) error {
 }
 
 // Wrapf returns an error annotating err with a stack trace
-// at the point Wrapf is call, and the format specifier.
+// at the point Wrapf is called, and the format specifier.
 // If err is nil, Wrapf returns nil.
 func Wrapf(err error, format string, args ...interface{}) error {
 	if err == nil {
@@ -220,6 +221,18 @@ func WithMessage(err error, message string) error {
 	}
 }
 
+// WithMessagef annotates err with the format specifier.
+// If err is nil, WithMessagef returns nil.
+func WithMessagef(err error, format string, args ...interface{}) error {
+	if err == nil {
+		return nil
+	}
+	return &withMessage{
+		cause: err,
+		msg:   fmt.Sprintf(format, args...),
+	}
+}
+
 type withMessage struct {
 	cause error
 	msg   string
diff --git a/errors_test.go b/errors_test.go
index 1d8c635..2089b2f 100644
--- a/errors_test.go
+++ b/errors_test.go
@@ -196,7 +196,32 @@ func TestWithMessage(t *testing.T) {
 			t.Errorf("WithMessage(%v, %q): got: %q, want %q", tt.err, tt.message, got, tt.want)
 		}
 	}
+}
+
+func TestWithMessagefNil(t *testing.T) {
+	got := WithMessagef(nil, "no error")
+	if got != nil {
+		t.Errorf("WithMessage(nil, \"no error\"): got %#v, expected nil", got)
+	}
+}
 
+func TestWithMessagef(t *testing.T) {
+	tests := []struct {
+		err     error
+		message string
+		want    string
+	}{
+		{io.EOF, "read error", "read error: EOF"},
+		{WithMessagef(io.EOF, "read error without format specifier"), "client error", "client error: read error without format specifier: EOF"},
+		{WithMessagef(io.EOF, "read error with %d format specifier", 1), "client error", "client error: read error with 1 format specifier: EOF"},
+	}
+
+	for _, tt := range tests {
+		got := WithMessagef(tt.err, tt.message).Error()
+		if got != tt.want {
+			t.Errorf("WithMessage(%v, %q): got: %q, want %q", tt.err, tt.message, got, tt.want)
+		}
+	}
 }
 
 // errors.New, etc values are not expected to be compared by value
diff --git a/format_test.go b/format_test.go
index 15fd7d8..c2eef5f 100644
--- a/format_test.go
+++ b/format_test.go
@@ -491,7 +491,7 @@ type wrapper struct {
 	want []string
 }
 
-func prettyBlocks(blocks []string, prefix ...string) string {
+func prettyBlocks(blocks []string) string {
 	var out []string
 
 	for _, b := range blocks {
diff --git a/stack.go b/stack.go
index 6b1f289..2874a04 100644
--- a/stack.go
+++ b/stack.go
@@ -46,7 +46,8 @@ func (f Frame) line() int {
 //
 // Format accepts flags that alter the printing of some verbs, as follows:
 //
-//    %+s   path of source file relative to the compile time GOPATH
+//    %+s   function name and path of source file relative to the compile time
+//          GOPATH separated by \n\t (<funcname>\n\t<path>)
 //    %+v   equivalent to %+s:%d
 func (f Frame) Format(s fmt.State, verb rune) {
 	switch verb {
@@ -79,6 +80,14 @@ func (f Frame) Format(s fmt.State, verb rune) {
 // StackTrace is stack of Frames from innermost (newest) to outermost (oldest).
 type StackTrace []Frame
 
+// Format formats the stack of Frames according to the fmt.Formatter interface.
+//
+//    %s	lists source files for each Frame in the stack
+//    %v	lists the source file and line number for each Frame in the stack
+//
+// Format accepts flags that alter the printing of some verbs, as follows:
+//
+//    %+v   Prints filename, function, and line number for each Frame in the stack.
 func (st StackTrace) Format(s fmt.State, verb rune) {
 	switch verb {
 	case 'v':
@@ -136,43 +145,3 @@ func funcname(name string) string {
 	i = strings.Index(name, ".")
 	return name[i+1:]
 }
-
-func trimGOPATH(name, file string) string {
-	// Here we want to get the source file path relative to the compile time
-	// GOPATH. As of Go 1.6.x there is no direct way to know the compiled
-	// GOPATH at runtime, but we can infer the number of path segments in the
-	// GOPATH. We note that fn.Name() returns the function name qualified by
-	// the import path, which does not include the GOPATH. Thus we can trim
-	// segments from the beginning of the file path until the number of path
-	// separators remaining is one more than the number of path separators in
-	// the function name. For example, given:
-	//
-	//    GOPATH     /home/user
-	//    file       /home/user/src/pkg/sub/file.go
-	//    fn.Name()  pkg/sub.Type.Method
-	//
-	// We want to produce:
-	//
-	//    pkg/sub/file.go
-	//
-	// From this we can easily see that fn.Name() has one less path separator
-	// than our desired output. We count separators from the end of the file
-	// path until it finds two more than in the function name and then move
-	// one character forward to preserve the initial path segment without a
-	// leading separator.
-	const sep = "/"
-	goal := strings.Count(name, sep) + 2
-	i := len(file)
-	for n := 0; n < goal; n++ {
-		i = strings.LastIndex(file[:i], sep)
-		if i == -1 {
-			// not enough separators found, set i so that the slice expression
-			// below leaves file unmodified
-			i = -len(sep)
-			break
-		}
-	}
-	// get back to 0 or trim the leading separator
-	file = file[i+len(sep):]
-	return file
-}
diff --git a/stack_test.go b/stack_test.go
index 510c27a..85fc419 100644
--- a/stack_test.go
+++ b/stack_test.go
@@ -146,24 +146,6 @@ func TestFuncname(t *testing.T) {
 	}
 }
 
-func TestTrimGOPATH(t *testing.T) {
-	var tests = []struct {
-		Frame
-		want string
-	}{{
-		Frame(initpc),
-		"github.com/pkg/errors/stack_test.go",
-	}}
-
-	for i, tt := range tests {
-		pc := tt.Frame.pc()
-		fn := runtime.FuncForPC(pc)
-		file, _ := fn.FileLine(pc)
-		got := trimGOPATH(fn.Name(), file)
-		testFormatRegexp(t, i, got, "%s", tt.want)
-	}
-}
-
 func TestStackTrace(t *testing.T) {
 	tests := []struct {
 		err  error
@@ -171,24 +153,24 @@ func TestStackTrace(t *testing.T) {
 	}{{
 		New("ooh"), []string{
 			"github.com/pkg/errors.TestStackTrace\n" +
-				"\t.+/github.com/pkg/errors/stack_test.go:172",
+				"\t.+/github.com/pkg/errors/stack_test.go:154",
 		},
 	}, {
 		Wrap(New("ooh"), "ahh"), []string{
 			"github.com/pkg/errors.TestStackTrace\n" +
-				"\t.+/github.com/pkg/errors/stack_test.go:177", // this is the stack of Wrap, not New
+				"\t.+/github.com/pkg/errors/stack_test.go:159", // this is the stack of Wrap, not New
 		},
 	}, {
 		Cause(Wrap(New("ooh"), "ahh")), []string{
 			"github.com/pkg/errors.TestStackTrace\n" +
-				"\t.+/github.com/pkg/errors/stack_test.go:182", // this is the stack of New
+				"\t.+/github.com/pkg/errors/stack_test.go:164", // this is the stack of New
 		},
 	}, {
 		func() error { return New("ooh") }(), []string{
 			`github.com/pkg/errors.(func·009|TestStackTrace.func1)` +
-				"\n\t.+/github.com/pkg/errors/stack_test.go:187", // this is the stack of New
+				"\n\t.+/github.com/pkg/errors/stack_test.go:169", // this is the stack of New
 			"github.com/pkg/errors.TestStackTrace\n" +
-				"\t.+/github.com/pkg/errors/stack_test.go:187", // this is the stack of New's caller
+				"\t.+/github.com/pkg/errors/stack_test.go:169", // this is the stack of New's caller
 		},
 	}, {
 		Cause(func() error {
@@ -197,11 +179,11 @@ func TestStackTrace(t *testing.T) {
 			}()
 		}()), []string{
 			`github.com/pkg/errors.(func·010|TestStackTrace.func2.1)` +
-				"\n\t.+/github.com/pkg/errors/stack_test.go:196", // this is the stack of Errorf
+				"\n\t.+/github.com/pkg/errors/stack_test.go:178", // this is the stack of Errorf
 			`github.com/pkg/errors.(func·011|TestStackTrace.func2)` +
-				"\n\t.+/github.com/pkg/errors/stack_test.go:197", // this is the stack of Errorf's caller
+				"\n\t.+/github.com/pkg/errors/stack_test.go:179", // this is the stack of Errorf's caller
 			"github.com/pkg/errors.TestStackTrace\n" +
-				"\t.+/github.com/pkg/errors/stack_test.go:198", // this is the stack of Errorf's caller's caller
+				"\t.+/github.com/pkg/errors/stack_test.go:180", // this is the stack of Errorf's caller's caller
 		},
 	}}
 	for i, tt := range tests {
@@ -271,19 +253,19 @@ func TestStackTraceFormat(t *testing.T) {
 	}, {
 		stackTrace()[:2],
 		"%v",
-		`\[stack_test.go:225 stack_test.go:272\]`,
+		`\[stack_test.go:207 stack_test.go:254\]`,
 	}, {
 		stackTrace()[:2],
 		"%+v",
 		"\n" +
 			"github.com/pkg/errors.stackTrace\n" +
-			"\t.+/github.com/pkg/errors/stack_test.go:225\n" +
+			"\t.+/github.com/pkg/errors/stack_test.go:207\n" +
 			"github.com/pkg/errors.TestStackTraceFormat\n" +
-			"\t.+/github.com/pkg/errors/stack_test.go:276",
+			"\t.+/github.com/pkg/errors/stack_test.go:258",
 	}, {
 		stackTrace()[:2],
 		"%#v",
-		`\[\]errors.Frame{stack_test.go:225, stack_test.go:284}`,
+		`\[\]errors.Frame{stack_test.go:207, stack_test.go:266}`,
 	}}
 
 	for i, tt := range tests {