Add CreateChild to create elements with continuations

Introduced the Element.CreateChild function to support the
creation of child elements with continuation functions.

etree.go

@@ -752,13 +752,34 @@ func (e *Element) findTermCharDataIndex(start int) int {
 }
 
 // CreateElement creates a new element with the specified tag (i.e., name) and
-// adds it as the last child token of this element. The tag may include a
-// prefix followed by a colon.
+// adds it as the last child of element 'e'. The tag may include a prefix
+// followed by a colon.
 func (e *Element) CreateElement(tag string) *Element {
 	space, stag := spaceDecompose(tag)
 	return newElement(space, stag, e)
 }
 
+// CreateChild performs the same task as CreateElement but calls a
+// continuation function after the child element is created, allowing
+// additional actions to be performed on the child element before returning.
+//
+// This method of element creation is particularly useful when building nested
+// XML documents from code. For example:
+//
+//	org := doc.CreateChild("organization", func(e *Element) {
+//		e.CreateComment("Mary")
+//		e.CreateChild("person", func(e *Element) {
+//			e.CreateAttr("name", "Mary")
+//			e.CreateAttr("age", "30")
+//			e.CreateAttr("hair", "brown")
+//		})
+//	})
+func (e *Element) CreateChild(tag string, cont func(e *Element)) *Element {
+	child := e.CreateElement(tag)
+	cont(child)
+	return child
+}
+
 // AddChild adds the token 't' as the last child of the element. If token 't'
 // was already the child of another element, it is first removed from its
 // parent element.

etree_test.go

@@ -1629,3 +1629,56 @@ func TestSiblingElement(t *testing.T) {
 		}
 	}
 }
+
+func TestContinuations(t *testing.T) {
+	doc := NewDocument()
+	root := doc.CreateChild("root", func(e *Element) {
+		e.CreateChild("child1", func(e *Element) {
+			e.CreateComment("Grandchildren of child #1")
+			e.CreateChild("grandchild1", func(e *Element) {
+				e.CreateAttr("attr1", "1")
+				e.CreateAttr("attr2", "2")
+			})
+			e.CreateChild("grandchild2", func(e *Element) {
+				e.CreateAttr("attr1", "3")
+				e.CreateAttr("attr2", "4")
+			})
+		})
+		e.CreateChild("child2", func(e *Element) {
+			e.CreateComment("Grandchildren of child #2")
+			e.CreateChild("grandchild1", func(e *Element) {
+				e.CreateAttr("attr1", "5")
+				e.CreateAttr("attr2", "6")
+			})
+			e.CreateChild("grandchild2", func(e *Element) {
+				e.CreateAttr("attr1", "7")
+				e.CreateAttr("attr2", "8")
+			})
+		})
+	})
+	checkStrEq(t, root.Tag, "root")
+
+	// Serialize the document to a string
+	doc.IndentTabs()
+	s, err := doc.WriteToString()
+	if err != nil {
+		t.Error("etree: failed to serialize document")
+	}
+
+	// Make sure the serialized XML matches expectation.
+	expected := `<root>
+	<child1>
+		<!--Grandchildren of child #1-->
+		<grandchild1 attr1="1" attr2="2"/>
+		<grandchild2 attr1="3" attr2="4"/>
+	</child1>
+	<child2>
+		<!--Grandchildren of child #2-->
+		<grandchild1 attr1="5" attr2="6"/>
+		<grandchild2 attr1="7" attr2="8"/>
+	</child2>
+</root>
+`
+
+	checkStrEq(t, s, expected)
+}