fix(code-editor): allow extension on nested elements

package.json

@@ -15,7 +15,6 @@
 			"yaml": ">=2.8.3",
 			"picomatch": ">=4.0.4",
 			"file-type": ">=21.3.2",
-			"brace-expansion": ">=2.0.3 <3",
 			"defu": ">=6.1.5",
 			"vite": "^8.1.5",
 			"esbuild@>=0.27.3 <0.28.1": "0.28.1",
@@ -25,7 +24,8 @@
 			"@xhmikosr/decompress@<10.2.1": "10.2.1",
 			"ws@>=8.0.0 <8.21.0": "8.21.1",
 			"@babel/core@<=7.29.0": "7.29.7",
-			"brace-expansion": "^5.0.7"
+			"brace-expansion@>=2.0.0 <2.1.4": "2.1.4",
+			"brace-expansion@>=3.0.0 <5.0.9": "5.0.9"
 		}
 	},
 	"devDependencies": {

packages/react-components/src/components/code-editor/fhir-autocomplete.ts

@@ -315,6 +315,10 @@ async function resolveElements(
 
 	let currentPath = resourceType;
 	let currentElements = result.elements;
+	// Whether the element the path currently points into is a BackboneElement
+	// (or a resource, at the root). BackboneElements and resources allow
+	// `modifierExtension`; plain complex datatypes (e.g. HumanName) do not.
+	let isBackbone = path.length === 0;
 
 	for (const key of path) {
 		if (key === "resourceType") return [];
@@ -324,6 +328,7 @@ async function resolveElements(
 
 		if (el.contentReference) {
 			currentPath = el.contentReference.replace(/^#/, "");
+			isBackbone = true;
 			continue;
 		}
 
@@ -332,13 +337,15 @@ async function resolveElements(
 
 		if (typeCode === "BackboneElement") {
 			currentPath = el.path;
+			isBackbone = true;
 			continue;
 		}
 
 		const typeResult = await collectAllElements(typeCode, getSDs);
 		if (!typeResult) return [];
 		currentPath = typeResult.basePath;
 		currentElements = typeResult.elements;
+		isBackbone = false;
 	}
 
 	const children = directChildren(currentElements, currentPath);
@@ -362,9 +369,36 @@ async function resolveElements(
 		}
 	}
 
+	// Every FHIR element allows `id` and `extension`; BackboneElements and
+	// resources additionally allow `modifierExtension`. StructureDefinition
+	// differentials don't repeat these inherited base-type elements for nested
+	// backbone/complex elements, so add them here (unless already present) so
+	// both autocomplete and validation see them.
+	appendUniversalElements(expanded, currentPath, isBackbone);
+
 	return expanded;
 }
 
+function appendUniversalElements(
+	elements: FhirElement[],
+	basePath: string,
+	isBackbone: boolean,
+): void {
+	const present = new Set(elements.map((el) => fieldName(el)));
+	const universal: { name: string; type: string }[] = [
+		{ name: "id", type: "string" },
+		{ name: "extension", type: "Extension" },
+	];
+	if (isBackbone) {
+		universal.push({ name: "modifierExtension", type: "Extension" });
+	}
+	for (const { name, type } of universal) {
+		if (!present.has(name)) {
+			elements.push({ path: `${basePath}.${name}`, type: [{ code: type }] });
+		}
+	}
+}
+
 async function findResourceBoundary(
 	path: string[],
 	resourceType: string,