Allow fragments to be used in DeadDocument.

They work like React.Fragment except we don't have components yet
so it has to be a special node.

src/commands/interface-manager/DeadDocument.ts

@@ -63,6 +63,7 @@ export enum NodeTag {
     BoldFace = 'b',
     ItalicFace = 'i',
     Anchor = 'a',
+    Fragment = 'fragment',
 }
 
 /**

src/commands/interface-manager/DeadDocumentHtml.ts

@@ -62,4 +62,7 @@ HTML_RENDERER.registerRenderer<FringeLeafRenderFunction<TransactionalOutputConte
         context.output.writeString('>')
     },
     staticString('</a>')
+).registerInnerNode(NodeTag.Fragment,
+    blank,
+    blank
 );

src/commands/interface-manager/DeadDocumentMarkdown.ts

@@ -132,4 +132,7 @@ MARKDOWN_RENDERER.registerRenderer<FringeLeafRenderFunction<TransactionalOutputC
         }
         context.output.writeString(`](${href})`);
     }
+).registerInnerNode(NodeTag.Fragment,
+    blank,
+    blank
 );

src/commands/interface-manager/JSXFactory.ts

@@ -23,8 +23,13 @@ export function JSXFactory(tag: NodeTag, properties: any, ...rawChildren: (Docum
             makeLeafNode<TextNode>(NodeTag.TextNode, node, (rawChild as number).toString());
         } else if (Array.isArray(rawChild)) {
             rawChild.forEach(ensureChild);
+        // Then it's a DocumentNode|LeafNode
         } else if (typeof rawChild.leafNode === 'boolean') {
-            node.addChild(rawChild);
+            if (rawChild.tag === NodeTag.Fragment) {
+                (rawChild as DocumentNode).getChildren().forEach(node.addChild, node);
+            } else {
+                node.addChild(rawChild);
+            }
         } else {
             const presentationType = presentationTypeOf(rawChild);
             if (presentationType !== undefined) {