Update docs.

README.md

@@ -34,3 +34,30 @@ type Enclosure interface {
 
 func Enclose(e Enclosure, w ...Widget) Widget { ... }
 ```
+
+The `Context` struct also contains a `map[string]interface{}` allowing arbitrary
+data to be maintained. This can be used, for example, to define themes, and control
+the operation of a `WidgetCombinator` during operation. For example>
+
+```go
+type fWidget struct { l Layout }
+func NewfWidget(l layout) fWidget { return fWidget{ l: l } }
+
+func (f Flex) Flexible(v float32) Widget {
+	return NewfWidget(func(ctx Context) Context {
+		ctx.extra["Flexible"] = v
+		return ctx
+	})
+}
+
+...
+	ctx = giowrap.LayoutWithContext(ctx,
+		myFlex(
+			w1,
+			giowrap.Flexible(0.5),
+			w2,
+			giowrap.Flexible(1),
+			w3,
+		))
+...
+```

cmd/hello/main.go

@@ -57,9 +57,9 @@ func main() {
 						OuterInset(
 						    f(
 							e1,
-							f.Flexible(5),
+							giowrap.Flexible(5),
 							InnerInset(e2),
-							f.Flexible(10),
+							giowrap.Flexible(10),
 							btn,
 						)))
 					ctx.Draw()

main.go

@@ -149,7 +149,7 @@ type FlexChild struct {
 
 type Flex WidgetCombinator
 
-func (f Flex) Flexible(v float32) Widget {
+func Flexible(v float32) Widget {
 	return NewfWidget(func(ctx Context) Context {
 		ctx.extra["Flexible"] = v
 		return ctx