diff --git a/toplabel/bytes.go b/toplabel/bytes.go
new file mode 100644
index 0000000..3619c5a
--- /dev/null
+++ b/toplabel/bytes.go
@@ -0,0 +1,44 @@
+package toplabel
+
+import (
+	"sourcecode.social/reiver/go-rfc2396/alpha"
+	"sourcecode.social/reiver/go-rfc2396/alphanum"
+)
+
+func Bytes(p []byte) (result []byte, rest []byte, ok bool) {
+
+	length := len(p)
+
+	if length < 1 {
+		return nil, p, false
+	}
+
+	{
+		p0 := p[0]
+
+		if !alpha.ByteIs(p0) {
+			return nil, p, false
+		}
+	}
+
+	{
+		for i,b := range p {
+			if !alphanum.ByteIs(b) && '-' != b {
+
+				if !alphanum.ByteIs(p[i-1]) {
+					return p[:i-1], p[i-1:], true
+				}
+
+				return p[:i], p[i:], true
+			}
+		}
+
+
+		if !alphanum.ByteIs(p[length-1]) {
+			return p[:length-1], p[length-1:], true
+		}
+
+
+		return p, nil, true
+	}
+}
diff --git a/toplabel/bytes_test.go b/toplabel/bytes_test.go
new file mode 100644
index 0000000..fec4250
--- /dev/null
+++ b/toplabel/bytes_test.go
@@ -0,0 +1,463 @@
+package toplabel_test
+
+import (
+	"testing"
+
+	"bytes"
+
+	"sourcecode.social/reiver/go-rfc2396/toplabel"
+)
+
+func TestBytes(t *testing.T) {
+
+	tests := []struct{
+		Value []byte
+		ExpectedResult []byte
+		ExpectedRest []byte
+		ExpectedOK bool
+	}{
+		{
+			Value: nil,
+			ExpectedResult: nil,
+			ExpectedRest: nil,
+			ExpectedOK: false,
+		},
+		{
+			Value: []byte(nil),
+			ExpectedResult: nil,
+			ExpectedRest: nil,
+			ExpectedOK: false,
+		},
+
+
+
+		{
+			Value: []byte{},
+			ExpectedResult: nil,
+			ExpectedRest: nil,
+			ExpectedOK: false,
+		},
+		{
+			Value: []byte(""),
+			ExpectedResult: nil,
+			ExpectedRest: nil,
+			ExpectedOK: false,
+		},
+
+
+
+		{
+			Value:          []byte("com"),
+			ExpectedResult: []byte("com"),
+			ExpectedRest: nil,
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("com/"),
+			ExpectedResult: []byte("com"),
+			ExpectedRest:      []byte("/"),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("com/once/twice/thrice/fource.php"),
+			ExpectedResult: []byte("com"),
+			ExpectedRest:      []byte("/once/twice/thrice/fource.php"),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("com."),
+			ExpectedResult: []byte("com"),
+			ExpectedRest:      []byte("."),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("com./"),
+			ExpectedResult: []byte("com"),
+			ExpectedRest:      []byte("./"),
+			ExpectedOK: true,
+		},
+
+
+
+		{
+			Value:          []byte("co"),
+			ExpectedResult: []byte("co"),
+			ExpectedRest: nil,
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("co/"),
+			ExpectedResult: []byte("co"),
+			ExpectedRest:     []byte("/"),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("co/once/twice/thrice/fource.php"),
+			ExpectedResult: []byte("co"),
+			ExpectedRest:     []byte("/once/twice/thrice/fource.php"),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("co."),
+			ExpectedResult: []byte("co"),
+			ExpectedRest:     []byte("."),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("co./"),
+			ExpectedResult: []byte("co"),
+			ExpectedRest:     []byte("./"),
+			ExpectedOK: true,
+		},
+
+
+
+		{
+			Value:          []byte("c"),
+			ExpectedResult: []byte("c"),
+			ExpectedRest: nil,
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("c/"),
+			ExpectedResult: []byte("c"),
+			ExpectedRest:    []byte("/"),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("c/once/twice/thrice/fource.php"),
+			ExpectedResult: []byte("c"),
+			ExpectedRest:    []byte("/once/twice/thrice/fource.php"),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("c."),
+			ExpectedResult: []byte("c"),
+			ExpectedRest:    []byte("."),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("c./"),
+			ExpectedResult: []byte("c"),
+			ExpectedRest:    []byte("./"),
+			ExpectedOK: true,
+		},
+
+
+
+		{
+			Value:          []byte("c-"),
+			ExpectedResult: []byte("c"),
+			ExpectedRest:    []byte("-"),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("c-/"),
+			ExpectedResult: []byte("c"),
+			ExpectedRest:    []byte("-/"),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("c-/once/twice/thrice/fource.php"),
+			ExpectedResult: []byte("c"),
+			ExpectedRest:    []byte("-/once/twice/thrice/fource.php"),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("c-."),
+			ExpectedResult: []byte("c"),
+			ExpectedRest:    []byte("-."),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("c-./"),
+			ExpectedResult: []byte("c"),
+			ExpectedRest:    []byte("-./"),
+			ExpectedOK: true,
+		},
+
+
+
+		{
+			Value:          []byte("c1"),
+			ExpectedResult: []byte("c1"),
+			ExpectedRest: nil,
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("c1/"),
+			ExpectedResult: []byte("c1"),
+			ExpectedRest:     []byte("/"),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("c1/once/twice/thrice/fource.php"),
+			ExpectedResult: []byte("c1"),
+			ExpectedRest:     []byte("/once/twice/thrice/fource.php"),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("c1."),
+			ExpectedResult: []byte("c1"),
+			ExpectedRest:     []byte("."),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("c1./"),
+			ExpectedResult: []byte("c1"),
+			ExpectedRest:     []byte("./"),
+			ExpectedOK: true,
+		},
+
+
+
+		{
+			Value:          []byte("c-1"),
+			ExpectedResult: []byte("c-1"),
+			ExpectedRest: nil,
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("c-1/"),
+			ExpectedResult: []byte("c-1"),
+			ExpectedRest:      []byte("/"),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("c-1/once/twice/thrice/fource.php"),
+			ExpectedResult: []byte("c-1"),
+			ExpectedRest:      []byte("/once/twice/thrice/fource.php"),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("c-1."),
+			ExpectedResult: []byte("c-1"),
+			ExpectedRest:      []byte("."),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("c-1./"),
+			ExpectedResult: []byte("c-1"),
+			ExpectedRest:      []byte("./"),
+			ExpectedOK: true,
+		},
+
+
+
+		{
+			Value:          []byte("c1-"),
+			ExpectedResult: []byte("c1"),
+			ExpectedRest:     []byte("-"),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("c1-/"),
+			ExpectedResult: []byte("c1"),
+			ExpectedRest:     []byte("-/"),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("c1-/once/twice/thrice/fource.php"),
+			ExpectedResult: []byte("c1"),
+			ExpectedRest:     []byte("-/once/twice/thrice/fource.php"),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("c1-."),
+			ExpectedResult: []byte("c1"),
+			ExpectedRest:     []byte("-."),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("c1-./"),
+			ExpectedResult: []byte("c1"),
+			ExpectedRest:     []byte("-./"),
+			ExpectedOK: true,
+		},
+	}
+
+	for b0:=byte('a'); b0 <= 'z'; b0++ {
+
+		{
+			test := struct{
+				Value []byte
+				ExpectedResult []byte
+				ExpectedRest []byte
+				ExpectedOK bool
+			}{
+				Value:          []byte{b0},
+				ExpectedResult: []byte{b0},
+				ExpectedRest: nil,
+				ExpectedOK: true,
+			}
+
+			tests = append(tests, test)
+		}
+
+		for b1:=byte('0'); b1 <= '9'; b1++ {
+
+			test := struct{
+				Value []byte
+				ExpectedResult []byte
+				ExpectedRest []byte
+				ExpectedOK bool
+			}{
+				Value:          []byte{b0,b1},
+				ExpectedResult: []byte{b0,b1},
+				ExpectedRest: nil,
+				ExpectedOK: true,
+			}
+
+			tests = append(tests, test)
+		}
+
+		for b1:=byte('A'); b1 <= 'Z'; b1++ {
+
+			test := struct{
+				Value []byte
+				ExpectedResult []byte
+				ExpectedRest []byte
+				ExpectedOK bool
+			}{
+				Value:          []byte{b0,b1},
+				ExpectedResult: []byte{b0,b1},
+				ExpectedRest: nil,
+				ExpectedOK: true,
+			}
+
+			tests = append(tests, test)
+		}
+
+		for b1:=byte('a'); b1 <= 'z'; b1++ {
+
+			test := struct{
+				Value []byte
+				ExpectedResult []byte
+				ExpectedRest []byte
+				ExpectedOK bool
+			}{
+				Value:          []byte{b0,b1},
+				ExpectedResult: []byte{b0,b1},
+				ExpectedRest: nil,
+				ExpectedOK: true,
+			}
+
+			tests = append(tests, test)
+		}
+	}
+
+	for b0:=byte('A'); b0 <= 'Z'; b0++ {
+
+		{
+			test := struct{
+				Value []byte
+				ExpectedResult []byte
+				ExpectedRest []byte
+				ExpectedOK bool
+			}{
+				Value:          []byte{b0},
+				ExpectedResult: []byte{b0},
+				ExpectedRest: nil,
+				ExpectedOK: true,
+			}
+
+			tests = append(tests, test)
+		}
+
+		for b1:=byte('0'); b1 <= '9'; b1++ {
+
+			test := struct{
+				Value []byte
+				ExpectedResult []byte
+				ExpectedRest []byte
+				ExpectedOK bool
+			}{
+				Value:          []byte{b0,b1},
+				ExpectedResult: []byte{b0,b1},
+				ExpectedRest: nil,
+				ExpectedOK: true,
+			}
+
+			tests = append(tests, test)
+		}
+
+		for b1:=byte('A'); b1 <= 'Z'; b1++ {
+
+			test := struct{
+				Value []byte
+				ExpectedResult []byte
+				ExpectedRest []byte
+				ExpectedOK bool
+			}{
+				Value:          []byte{b0,b1},
+				ExpectedResult: []byte{b0,b1},
+				ExpectedRest: nil,
+				ExpectedOK: true,
+			}
+
+			tests = append(tests, test)
+		}
+
+		for b1:=byte('a'); b1 <= 'z'; b1++ {
+
+			test := struct{
+				Value []byte
+				ExpectedResult []byte
+				ExpectedRest []byte
+				ExpectedOK bool
+			}{
+				Value:          []byte{b0,b1},
+				ExpectedResult: []byte{b0,b1},
+				ExpectedRest: nil,
+				ExpectedOK: true,
+			}
+
+			tests = append(tests, test)
+		}
+	}
+
+	for testNumber, test := range tests {
+
+		actualResult, actualRest, actualOK := toplabel.Bytes(test.Value)
+
+		{
+			expected := test.ExpectedOK
+			actual   := actualOK
+
+			if expected != actual {
+				t.Errorf("For test #%d, the actual ok-result is not what was expected.", testNumber)
+				t.Logf("EXPECTED: %t", expected)
+				t.Logf("ACTUAL:   %t", actual)
+				t.Logf("VALUE: %q", test.Value)
+				continue
+			}
+		}
+
+		{
+			expected := test.ExpectedResult
+			actual   := actualResult
+
+			if !bytes.Equal(expected, actual) {
+				t.Errorf("For test #%d, the actual result is not what was expected.", testNumber)
+				t.Logf("EXPECTED: %q (%#v)", expected, expected)
+				t.Logf("ACTUAL:   %q (%#v)", actual, actual)
+				t.Logf("VALUE: %q", test.Value)
+				t.Logf("ACTUAL-REST: %q (%#v)", actualRest, actualRest)
+				continue
+			}
+		}
+
+		{
+			expected := test.ExpectedRest
+			actual   := actualRest
+
+			if !bytes.Equal(expected, actual) {
+				t.Errorf("For test #%d, the actual rest is not what was expected.", testNumber)
+				t.Logf("EXPECTED: %q (%#v)", expected, expected)
+				t.Logf("ACTUAL:   %q (%#v)", actual, actual)
+				t.Logf("VALUE: %q", test.Value)
+				continue
+			}
+		}
+	}
+}