diff --git a/init.go b/init.go
index 88e5cdd..524caf5 100644
--- a/init.go
+++ b/init.go
@@ -1,10 +1,5 @@
 package xerror
 
-// func caller depth
-const (
-	callDepth = 3
-)
-
 var (
 	// ErrDone done
 	ErrDone        = New("DONE")
diff --git a/util.go b/util.go
index d2c1897..2c6c9c6 100644
--- a/util.go
+++ b/util.go
@@ -20,7 +20,7 @@ func handleErr(err *error, _err interface{}) {
 	case string:
 		*err = errors.New(_err)
 	default:
-		*err = New(ErrUnknownType.Code, fmt.Sprintf("%+v", _err))
+		*err = WrapF(ErrUnknownType, "%+v", _err)
 	}
 }
 
@@ -31,7 +31,7 @@ func handle(err error, msg string, args ...interface{}) *xerror {
 
 	err2 := &xerror{}
 	err2.Msg = msg
-	err2.Caller = callerWithDepth(callDepth + 1)
+	err2.Caller = callerWithDepth(xerror_core.CallDepth + 1)
 	err2.Cause1 = err
 	return err2
 }
@@ -45,7 +45,7 @@ func callerWithDepth(callDepths ...int) string {
 		return ""
 	}
 
-	var cd = callDepth
+	var cd = xerror_core.CallDepth
 	if len(callDepths) > 0 {
 		cd = callDepths[0]
 	}
@@ -58,7 +58,7 @@ func callerWithDepth(callDepths ...int) string {
 	f := frame(pcs[0])
 	fn := runtime.FuncForPC(f.pc())
 	if fn == nil {
-		return "unknown type"
+		return ErrUnknownType.Error()
 	}
 
 	file, line := fn.FileLine(f.pc())
@@ -67,7 +67,7 @@ func callerWithDepth(callDepths ...int) string {
 
 func callerWithFunc(fn reflect.Value) string {
 	if !fn.IsValid() || fn.IsNil() || fn.Kind() != reflect.Func {
-		panic(ErrNotFuncType)
+		Panic(ErrNotFuncType)
 	}
 	var _fn = fn.Pointer()
 	var file, line = runtime.FuncForPC(_fn).FileLine(_fn)
diff --git a/xerror.go b/xerror.go
index d4edd81..451aa2c 100644
--- a/xerror.go
+++ b/xerror.go
@@ -2,6 +2,7 @@ package xerror
 
 import (
 	"fmt"
+	"github.com/pubgo/xerror/xerror_core"
 	"net/http"
 	"os"
 	"reflect"
@@ -28,7 +29,7 @@ func New(code string, ms ...string) *xerrorBase {
 	xw := &xerrorBase{}
 	xw.Code = code
 	xw.Msg = msg
-	xw.Caller = callerWithDepth(callDepth)
+	xw.Caller = callerWithDepth(xerror_core.CallDepth)
 
 	return xw
 }
@@ -58,7 +59,7 @@ func Resp(f func(err XErr)) {
 		f(err.(XErr))
 		return
 	}
-	f(&xerror{Cause1: err, Caller: callerWithDepth(callDepth + 1)})
+	f(&xerror{Cause1: err, Caller: callerWithDepth(xerror_core.CallDepth + 1)})
 }
 
 func RespExit() {
diff --git a/xerror_color.go b/xerror_color.go
index d298593..0086328 100644
--- a/xerror_color.go
+++ b/xerror_color.go
@@ -2,8 +2,11 @@ package xerror
 
 import "fmt"
 
+// Color represents a text color.
+type color uint8
+
 const (
-	colorBlack = iota + 30
+	colorBlack color = iota + 30
 	colorRed
 	colorGreen
 	colorYellow
@@ -11,11 +14,11 @@ const (
 	colorMagenta
 	colorCyan
 	colorWhite
-
-	colorBold     = 1
-	colorDarkGray = 90
+	colorBold     color = 1
+	colorDarkGray color = 90
 )
 
-func colorize(s interface{}, c int) string {
-	return fmt.Sprintf("\x1b[%dm%v\x1b[0m", c, s)
+// Add adds the coloring to the given string.
+func (c color) P(s string, args ...interface{}) string {
+	return fmt.Sprintf("\x1b[%dm%s\x1b[0m", uint8(c), fmt.Sprintf(s, args...))
 }
diff --git a/xerror_core/core.go b/xerror_core/core.go
index 80b6e80..7f0d5cd 100644
--- a/xerror_core/core.go
+++ b/xerror_core/core.go
@@ -1,6 +1,7 @@
 package xerror_core
 
 var IsCaller bool
+var CallDepth = 3
 
 func init() {
 	IsCaller = true
diff --git a/xrr.go b/xrr.go
index c2a49cd..be57065 100644
--- a/xrr.go
+++ b/xrr.go
@@ -3,12 +3,13 @@ package xerror
 import (
 	"encoding/json"
 	"fmt"
+	"github.com/pubgo/xerror/xerror_core"
 	"io"
 	"strings"
 )
 
 type xerrorBase struct {
-	Code  string `json:"code,omitempty"`
+	Code   string `json:"code,omitempty"`
 	Msg    string `json:"msg,omitempty"`
 	Caller string `json:"caller,omitempty"`
 }
@@ -27,7 +28,7 @@ func (t *xerrorBase) New(code string, ms ...string) error {
 	xw := &xerrorBase{}
 	xw.Code = code
 	xw.Msg = msg
-	xw.Caller = callerWithDepth(callDepth)
+	xw.Caller = callerWithDepth(xerror_core.CallDepth)
 
 	return xw
 }
@@ -72,15 +73,15 @@ func (t *xerror) p() string {
 	for xrr != nil {
 		buf.WriteString("========================================================================================================================\n")
 		if xrr.Cause1 != nil {
-			buf.WriteString(fmt.Sprintf("   %s]: %s\n", colorize("Err", colorRed), xrr.Cause1))
+			buf.WriteString(fmt.Sprintf("   %s]: %s\n", colorRed.P("Err"), xrr.Cause1))
 		}
 		if xrr.Msg != "" {
-			buf.WriteString(fmt.Sprintf("   %s]: %s\n", colorize("Msg", colorGreen), xrr.Msg))
+			buf.WriteString(fmt.Sprintf("   %s]: %s\n", colorGreen.P("Msg"), xrr.Msg))
 		}
 		if xrr.Code1 != "" {
-			buf.WriteString(fmt.Sprintf("  %s]: %s\n", colorize("Code", colorGreen), xrr.Code1))
+			buf.WriteString(fmt.Sprintf("  %s]: %s\n", colorGreen.P("Code"), xrr.Code1))
 		}
-		buf.WriteString(fmt.Sprintf("%s]: %s\n", colorize("Caller", colorYellow), xrr.Caller))
+		buf.WriteString(fmt.Sprintf("%s]: %s\n", colorYellow.P("Caller"), xrr.Caller))
 		xrr = trans(xrr.Cause1)
 	}
 	buf.WriteString("========================================================================================================================\n\n")
@@ -93,6 +94,8 @@ func (t *xerror) Is(err error) bool {
 	}
 
 	switch err := err.(type) {
+	case *xerrorBase:
+		return err == t.Cause1 || err.Code == t.Code1
 	case *xerror:
 		return err == t || err.Cause1 == t.Cause1 || err.Code1 == t.Code1
 	case error:
@@ -108,6 +111,8 @@ func (t *xerror) As(err interface{}) bool {
 	}
 
 	switch e := err.(type) {
+	case *xerrorBase:
+		return strings.HasPrefix(t.Code1, e.Code)
 	case *xerror:
 		return strings.HasPrefix(t.Code1, e.Code1)
 	case error: