Better transformation guide

documentation/docs/guides/transformation.mdx

@@ -35,14 +35,17 @@ func (u *User) InTransform(ctx context.Context) error {
 	u.LastName = strings.TrimSpace(u.LastName)
 	return nil
 }
+
+var _ fuego.InTransformer = (*User)(nil) // Ensure *User implements fuego.InTransformer
+// This check is a classic example of Go's interface implementation check and we highly recommand to use it 
 ```
 
 In the example above, we have a `User` struct with two fields: `FirstName` and `LastName`. We also have a method called `InTransform` that takes a `context.Context` and returns an `error`. This method is called before the data is unmarshaled into the `User` struct. In this method, we are transforming the `FirstName` to uppercase and trimming any whitespace from the `LastName`.
 
 When using the following controller, the data will be transformed before it is unmarshaled into the `User` struct.
 
 ```go
-func myController(c fuego.ContextWithBody[User]) (User, error) {
+func echoCapitalized(c fuego.ContextWithBody[User]) (User, error) {
 	user, err := c.Body()
 	if err != nil {
 		return User{}, err
@@ -53,3 +56,40 @@ func myController(c fuego.ContextWithBody[User]) (User, error) {
 	return u, nil
 }
 ```
+
+## Recursion
+
+Transformation is **not recursive**. If you have nested structs, you will need to transform each struct individually. This is done **on purpose** to give you more control over the transformation process: no assumptions are made about how you want to transform your data, no "magic".
+
+```go
+type Address struct {
+	Street string `json:"street"`
+	City   string `json:"city"`
+}
+
+func (a *Address) InTransform(ctx context.Context) error {
+	a.Street = strings.TrimSpace(a.Street)
+	a.City = strings.ToUpper(a.City)
+	return nil
+}
+
+type User struct {
+	FirstName string `json:"first_name"`
+	LastName  string `json:"last_name"`
+	// highlight-next-line
+	Address   Address `json:"address"` // Nested struct
+}
+
+func (u *User) InTransform(ctx context.Context) error {
+	u.FirstName = strings.ToUpper(u.FirstName)
+	u.LastName = strings.TrimSpace(u.LastName)
+
+// highlight-next-line
+	err := u.Address.InTransform(ctx) // Transform the nested struct
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+```

documentation/src/components/FlowChart.js

@@ -32,6 +32,7 @@ subgraph fuego
  click ErrorHandler "/fuego/docs/guides/errors" "Error Handling"
 end
 
+ErrorHandler -- JSON{b:'Error!'} --> resp(Response)
 Serialization -- JSON{b:'My Response!'} --> resp(Response)
 Controller -. JSON{b:'Custom Response!'} .-> resp(Response)