diff --git a/errorx.go b/errorx.go
index 287cb16..c65254f 100644
--- a/errorx.go
+++ b/errorx.go
@@ -6,6 +6,10 @@ import (
 	"strings"
 )
 
+// Newf returns an error according to a format specifier and param.
+// Each call to New returns a distinct error value even if the text is identical.
+//
+// If tracing is enabled then stacktrace is attached to the returned error.
 func Newf(format string, a ...any) error {
 	// NOTE: go vet printf check doesn't understand inverse expression.
 	if !IsTracingEnabled() || strings.Contains(format, "%w") {
@@ -32,11 +36,19 @@ func As(err error, target any) bool {
 	return errors.As(err, target)
 }
 
+// Into is type-safe alternative to [errorx.As].
+func Into[T error](err error) (T, bool) {
+	var dst T
+	ok := As(err, &dst)
+	return dst, ok
+}
+
 // Unwrap is just [errors.Unwrap].
 func Unwrap(err error) error {
 	return errors.Unwrap(err)
 }
 
+// IsAny is just a multiple [errors.Is] calls.
 func IsAny(err, target error, targets ...error) bool {
 	if errors.Is(err, target) {
 		return true
@@ -50,6 +62,14 @@ func IsAny(err, target error, targets ...error) bool {
 	return false
 }
 
+// Must returns value or panic if the error is non-nil.
+func Must[T any](v T, err error) T {
+	if err != nil {
+		panic(err)
+	}
+	return v
+}
+
 // errorString same as [errors.errorString] but with a frame field.
 type errorString struct {
 	s     string
diff --git a/frame.go b/frame.go
index 98a6525..a24257e 100644
--- a/frame.go
+++ b/frame.go
@@ -33,6 +33,9 @@ func (f Frame) Format(p Printer) {
 	}
 }
 
+// Caller returns a Frame that describes a frame on the caller's stack.
+// The argument skip is the number of frames to skip over.
+// Caller(0) returns the frame for the caller of Caller.
 func caller(skip int) Frame {
 	var s Frame
 	runtime.Callers(skip+1, s.frames[:])