diff --git a/README.md b/README.md
index 1b8082f9..0a19baa9 100644
--- a/README.md
+++ b/README.md
@@ -3,7 +3,7 @@
 Gio implements portable immediate mode GUI programs in Go. Gio programs run on all the major platforms:
 iOS/tvOS, Android, Linux (Wayland), macOS and Windows.
 
-[![GoDoc](https://godoc.org/gioui.org/ui/app?status.svg)](https://godoc.org/gioui.org/ui/app)
+[![GoDoc](https://godoc.org/gioui.org/ui?status.svg)](https://godoc.org/gioui.org/ui)
 
 ## Quickstart
 
diff --git a/ui/doc.go b/ui/doc.go
new file mode 100644
index 00000000..1042c623
--- /dev/null
+++ b/ui/doc.go
@@ -0,0 +1,9 @@
+/*
+
+Package ui implements portable desktop and mobile GUI programs.
+
+See https://gioui.org for instructions to setup dependencies and
+run Gio programs.
+
+*/
+package ui
diff --git a/ui/ui.go b/ui/ui.go
index db4370c6..579b0e47 100644
--- a/ui/ui.go
+++ b/ui/ui.go
@@ -8,26 +8,52 @@ import (
 	"gioui.org/ui/f32"
 )
 
+// Config contain the context for updating and
+// drawing a user interface.
 type Config struct {
+	// Device pixels per dp.
 	PxPerDp float32
+	// Device pixels per sp.
 	PxPerSp float32
-	Now     time.Time
+	// The current time for animation.
+	Now time.Time
 }
 
+// Pixels converts a value to unitless device pixels.
+func (c *Config) Pixels(v Value) float32 {
+	switch v.U {
+	case UnitPx:
+		return v.V
+	case UnitDp:
+		return c.PxPerDp * v.V
+	case UnitSp:
+		return c.PxPerSp * v.V
+	default:
+		panic("unknown unit")
+	}
+}
+
+// Op is implemented by all known drawing and control
+// operations.
 type Op interface {
 	ImplementsOp()
 }
 
+// OpLayer represents a semantic layer of UI.
 type OpLayer struct {
 	Op Op
 }
 
+// OpRedraw requests a redraw at the given time. Use
+// the zero value to request an immediate redraw.
 type OpRedraw struct {
 	At time.Time
 }
 
+// Ops is the operation for a list of ops.
 type Ops []Op
 
+// OpTransform transforms an op.
 type OpTransform struct {
 	Transform Transform
 	Op        Op
diff --git a/ui/unit.go b/ui/unit.go
index 33ba3222..f874fa27 100644
--- a/ui/unit.go
+++ b/ui/unit.go
@@ -2,16 +2,24 @@
 
 package ui
 
+// Value is a value with a unit.
 type Value struct {
 	V float32
 	U Unit
 }
 
+// Unit represents a unit for a Value.
 type Unit uint8
 
 const (
+	// UnitPx represent device pixels in the resolution of
+	// the underlying display.
 	UnitPx Unit = iota
+	// UnitDp represents device independent pixels. 1 dp will
+	// have the same apparent size across platforms and
+	// display resolutions.
 	UnitDp
+	// UnitSp is like UnitDp but for font sizes.
 	UnitSp
 )
 
@@ -26,16 +34,3 @@ func Dp(v float32) Value {
 func Sp(v float32) Value {
 	return Value{V: v, U: UnitSp}
 }
-
-func (c *Config) Pixels(v Value) float32 {
-	switch v.U {
-	case UnitPx:
-		return v.V
-	case UnitDp:
-		return c.PxPerDp * v.V
-	case UnitSp:
-		return c.PxPerSp * v.V
-	default:
-		panic("unknown unit")
-	}
-}