feat(html): add aria-expanded helper

Co-Authored-By: Virgil <virgil@lethean.io>

docs/architecture.md

@@ -42,6 +42,7 @@ Accessibility-oriented helpers are also provided for common attribute patterns:
 - `Dir(node, direction)`
 - `Alt(node, text)`
 - `AriaHidden(node, hidden)`
+- `AriaExpanded(node, expanded)`
 - `TabIndex(node, index)`
 - `AutoFocus(node)`
 

node.go

@@ -230,6 +230,15 @@ func AriaHidden(n Node, hidden bool) Node {
 	return n
 }
 
+// node.go: AriaExpanded sets the aria-expanded attribute on an element node.
+// Example: AriaExpanded(El("button"), true).
+func AriaExpanded(n Node, expanded bool) Node {
+	if expanded {
+		return Attr(n, "aria-expanded", "true")
+	}
+	return Attr(n, "aria-expanded", "false")
+}
+
 // node.go: TabIndex sets the tabindex attribute on an element node.
 // Example: TabIndex(El("button"), 0).
 func TabIndex(n Node, index int) Node {

node_test.go

@@ -330,6 +330,22 @@ func TestAriaHiddenHelper(t *testing.T) {
 	}
 }
 
+func TestAriaExpandedHelper(t *testing.T) {
+	ctx := NewContext()
+
+	expanded := AriaExpanded(El("button", Raw("menu")), true)
+	gotExpanded := expanded.Render(ctx)
+	if !strings.Contains(gotExpanded, `aria-expanded="true"`) {
+		t.Errorf("AriaExpanded(true) = %q, want aria-expanded=\"true\"", gotExpanded)
+	}
+
+	collapsed := AriaExpanded(El("button", Raw("menu")), false)
+	gotCollapsed := collapsed.Render(ctx)
+	if !strings.Contains(gotCollapsed, `aria-expanded="false"`) {
+		t.Errorf("AriaExpanded(false) = %q, want aria-expanded=\"false\"", gotCollapsed)
+	}
+}
+
 func TestTabIndexHelper(t *testing.T) {
 	ctx := NewContext()
 	node := TabIndex(El("button", Raw("action")), -1)