diff --git a/internal/client.go b/internal/client.go
index 7c42e41..6ecb703 100644
--- a/internal/client.go
+++ b/internal/client.go
@@ -10,47 +10,6 @@ import (
 	"path"
 )
 
-// Depth indicates whether a request applies to the resource's members. It's
-// defined in RFC 4918 section 10.2.
-type Depth int
-
-const (
-	// DepthZero indicates that the request applies only to the resource.
-	DepthZero Depth = 0
-	// DepthOne indicates that the request applies to the resource and its
-	// internal members only.
-	DepthOne Depth = 1
-	// DepthInfinity indicates that the request applies to the resource and all
-	// of its members.
-	DepthInfinity Depth = -1
-)
-
-// ParseDepth parses a Depth header.
-func ParseDepth(s string) (Depth, error) {
-	switch s {
-	case "0":
-		return DepthZero, nil
-	case "1":
-		return DepthOne, nil
-	case "infinity":
-		return DepthInfinity, nil
-	}
-	return 0, fmt.Errorf("webdav: invalid Depth value")
-}
-
-// String formats the depth.
-func (d Depth) String() string {
-	switch d {
-	case DepthZero:
-		return "0"
-	case DepthOne:
-		return "1"
-	case DepthInfinity:
-		return "infinity"
-	}
-	panic("webdav: invalid Depth value")
-}
-
 type Client struct {
 	http               *http.Client
 	endpoint           *url.URL
diff --git a/internal/internal.go b/internal/internal.go
new file mode 100644
index 0000000..cebbbfa
--- /dev/null
+++ b/internal/internal.go
@@ -0,0 +1,47 @@
+// Package internal provides low-level helpers for WebDAV clients and servers.
+package internal
+
+import (
+	"fmt"
+)
+
+// Depth indicates whether a request applies to the resource's members. It's
+// defined in RFC 4918 section 10.2.
+type Depth int
+
+const (
+	// DepthZero indicates that the request applies only to the resource.
+	DepthZero Depth = 0
+	// DepthOne indicates that the request applies to the resource and its
+	// internal members only.
+	DepthOne Depth = 1
+	// DepthInfinity indicates that the request applies to the resource and all
+	// of its members.
+	DepthInfinity Depth = -1
+)
+
+// ParseDepth parses a Depth header.
+func ParseDepth(s string) (Depth, error) {
+	switch s {
+	case "0":
+		return DepthZero, nil
+	case "1":
+		return DepthOne, nil
+	case "infinity":
+		return DepthInfinity, nil
+	}
+	return 0, fmt.Errorf("webdav: invalid Depth value")
+}
+
+// String formats the depth.
+func (d Depth) String() string {
+	switch d {
+	case DepthZero:
+		return "0"
+	case DepthOne:
+		return "1"
+	case DepthInfinity:
+		return "infinity"
+	}
+	panic("webdav: invalid Depth value")
+}