diff --git a/.github/workflows/swift.yml b/.github/workflows/swift.yml
index 68f627b..24b5d40 100644
--- a/.github/workflows/swift.yml
+++ b/.github/workflows/swift.yml
@@ -31,7 +31,7 @@ jobs:
       - name: Select latest available Xcode
         uses: maxim-lobanov/setup-xcode@v1.2.1
         with:
-          xcode-version: 12.2
+          xcode-version: 13.2.1
       - name: Checkout Repository
         uses: actions/checkout@v2
       - name: Build Swift Debug Package
diff --git a/Sources/DocCArchive/Schema_0_1/Document.swift b/Sources/DocCArchive/Schema_0_1/Document.swift
index 50a4132..baaf2e4 100644
--- a/Sources/DocCArchive/Schema_0_1/Document.swift
+++ b/Sources/DocCArchive/Schema_0_1/Document.swift
@@ -64,7 +64,7 @@ extension DocCArchive.DocCSchema_0_1 {
     
     public var schemaVersion          : SchemaVersion
     public var identifier             : Identifier
-    public var documentVersion        : Int?
+    public var documentVersion        : Int? // was 0, not set in 13.2.1
     public var kind                   : Kind
     public var metadata               : MetaData
     public var hierarchy              : Hierarchy
diff --git a/Sources/DocCArchive/Schema_0_1/References/ImageReference.swift b/Sources/DocCArchive/Schema_0_1/References/ImageReference.swift
index ebad9fa..0027969 100644
--- a/Sources/DocCArchive/Schema_0_1/References/ImageReference.swift
+++ b/Sources/DocCArchive/Schema_0_1/References/ImageReference.swift
@@ -27,9 +27,9 @@ extension DocCArchive.DocCSchema_0_1 {
       }
       
       public var url    : String // it's a path, not a URL
-      public var size   : Size
+      public var size   : Size?  // size is gone in 13.2.1 as per Issue 5
       public var traits : [ Trait ] // TBD: make Set?
-      
+
       func numberOfMatches(against requestedTraits: Set<Trait>) -> Int {
         var matchCount = 0
         for trait in requestedTraits {
@@ -39,7 +39,9 @@ extension DocCArchive.DocCSchema_0_1 {
       }
 
       public var description: String {
-        var ms = "<Variant: \(size) traits="
+        var ms = "<Variant:"
+        if let size = size { ms += " \(size)" }
+        ms += " traits="
         ms += traits.map({ $0.rawValue }).joined(separator: ",")
         ms += " " + url
         ms += ">"
diff --git a/Tests/DocCArchiveTests/DocumentDecodingTests.swift b/Tests/DocCArchiveTests/DocumentDecodingTests.swift
index ef9d5a8..f9640cb 100644
--- a/Tests/DocCArchiveTests/DocumentDecodingTests.swift
+++ b/Tests/DocCArchiveTests/DocumentDecodingTests.swift
@@ -33,20 +33,20 @@ final class DocumentDecodingTests: XCTestCase {
       document = try JSONDecoder().decode(DocCArchive.Document.self, from: data)
 
       guard let section = document.primaryContentSections?.first else {
-        XCTAssert(false, "did not find primary content section"); return
+        XCTFail("did not find primary content section"); return
       }
       guard case .content(let contents) = section.kind else {
-        XCTAssert(false, "did not find content section"); return
+        XCTFail("did not find content section"); return
       }
       guard case .aside(style: let style, content: let asideContents) = contents.dropFirst().first else {
-        XCTAssert(false, "did not find aside"); return
+        XCTFail("did not find aside"); return
       }
       XCTAssertEqual(style, .warning, "expected to find warning")
       XCTAssert(asideContents.count == 1)
     }
     catch {
       print("ERROR:", error)
-      XCTAssert(false, "failed to decode: \(error)")
+      XCTFail("failed to decode: \(error)")
       return
     }
     XCTAssertEqual(document.schemaVersion, .init(major: 0, minor: 1, patch: 0))
@@ -63,23 +63,23 @@ final class DocumentDecodingTests: XCTestCase {
       document = try JSONDecoder().decode(DocCArchive.Document.self, from: data)
       
       guard let section = document.primaryContentSections?.first else {
-        XCTAssert(false, "did not find primary content section"); return
+        XCTFail("did not find primary content section"); return
       }
       guard case .content(let contents) = section.kind else {
-        XCTAssert(false, "did not find content section"); return
+        XCTFail("did not find content section"); return
       }
       guard case .unorderedList(let list) = contents.dropFirst().first else {
-        XCTAssert(false, "did not find list"); return
+        XCTFail("did not find list"); return
       }
       XCTAssertEqual(list.count, 2)
       guard case .paragraph(let inlineContent) = list.last?.content.first else {
-        XCTAssert(false, "did not find paragraph"); return
+        XCTFail("did not find paragraph"); return
       }
       XCTAssertEqual(inlineContent.count, 2)
       guard case .reference(let id, let isActive, let ot, let otc) =
                     inlineContent.last else
       {
-        XCTAssert(false, "did not find reference"); return
+        XCTFail("did not find reference"); return
       }
       XCTAssertTrue(isActive)
       XCTAssertEqual(id, DocCArchive.DocCSchema_0_1.Identifier(
@@ -89,7 +89,7 @@ final class DocumentDecodingTests: XCTestCase {
     }
     catch {
       print("ERROR:", error)
-      XCTAssert(false, "failed to decode: \(error)")
+      XCTFail("failed to decode: \(error)")
       return
     }
     XCTAssertEqual(document.schemaVersion, .init(major: 0, minor: 1, patch: 0))
@@ -107,7 +107,7 @@ final class DocumentDecodingTests: XCTestCase {
     }
     catch {
       print("ERROR:", error)
-      XCTAssert(false, "failed to decode: \(error)")
+      XCTFail("failed to decode: \(error)")
       return
     }
     XCTAssertEqual(document.schemaVersion, .init(major: 0, minor: 1, patch: 0))
@@ -125,7 +125,7 @@ final class DocumentDecodingTests: XCTestCase {
     }
     catch {
       print("ERROR:", error)
-      XCTAssert(false, "failed to decode: \(error)")
+      XCTFail("failed to decode: \(error)")
       return
     }
     XCTAssertEqual(document.schemaVersion, .init(major: 0, minor: 1, patch: 0))
@@ -143,7 +143,7 @@ final class DocumentDecodingTests: XCTestCase {
     }
     catch {
       print("ERROR:", error)
-      XCTAssert(false, "failed to decode: \(error)")
+      XCTFail("failed to decode: \(error)")
       return
     }
     XCTAssertEqual(document.schemaVersion, .init(major: 0, minor: 1, patch: 0))
@@ -161,7 +161,7 @@ final class DocumentDecodingTests: XCTestCase {
     }
     catch {
       print("ERROR:", error)
-      XCTAssert(false, "failed to decode: \(error)")
+      XCTFail("failed to decode: \(error)")
       return
     }
     
@@ -199,7 +199,7 @@ final class DocumentDecodingTests: XCTestCase {
         XCTAssertEqual(hero.content.count          , 1)
         XCTAssertNil  (hero.action)
       }
-      else { XCTAssert(false, "Expected hero as the first section") }
+      else { XCTFail("Expected hero as the first section") }
     }
     if let section = document.sections.last {
       XCTAssertNil  (section.title)
@@ -228,7 +228,7 @@ final class DocumentDecodingTests: XCTestCase {
           }
         }
       }
-      else { XCTAssert(false, "Expected tasks as the last section") }
+      else { XCTFail("Expected tasks as the last section") }
     }
   }
 
@@ -241,14 +241,14 @@ final class DocumentDecodingTests: XCTestCase {
                       "~/Downloads directory")
     
     guard let de = fm.enumerator(atPath: dataDir.path) else {
-      XCTAssert(false, "did not get dir enum"); return
+      XCTFail("did not get dir enum"); return
     }
     
     var testCount = 0
     print("Parse files:")
     for p in de {
       guard let path = p as? String else {
-        XCTAssert(false, "expected path"); return
+        XCTFail("expected path"); return
       }
       guard !path.contains(".git")            else { continue }
       guard path.hasSuffix(".json")           else { continue }
@@ -268,13 +268,16 @@ final class DocumentDecodingTests: XCTestCase {
       }
       catch {
         print("ERROR:", error)
-        XCTAssert(false, "failed to decode: \(error)")
+        XCTFail("failed to decode: \(error)")
         return
       }
 
       XCTAssertEqual(document.schemaVersion,
                      .init(major: 0, minor: 1, patch: 0))
-      XCTAssertEqual(document.documentVersion, 0)
+      
+      // was 0, not set in 13.2.1
+      XCTAssert(document.documentVersion == 0 ||
+                document.documentVersion == nil)
     }
 
     print("# passing tests:", testCount)
@@ -290,14 +293,14 @@ final class DocumentDecodingTests: XCTestCase {
                       "~/Downloads directory")
     
     guard let de = fm.enumerator(atPath: dataDir.path) else {
-      XCTAssert(false, "did not get dir enum"); return
+      XCTFail("did not get dir enum"); return
     }
     
     var testCount = 0
     print("Parse files:")
     for p in de {
       guard let path = p as? String else {
-        XCTAssert(false, "expected path"); return
+        XCTFail("expected path"); return
       }
       guard !path.contains(".git")            else { continue }
       guard path.hasSuffix(".json")           else { continue }
@@ -317,7 +320,7 @@ final class DocumentDecodingTests: XCTestCase {
       }
       catch {
         print("ERROR:", error)
-        XCTAssert(false, "failed to decode: \(error)")
+        XCTFail("failed to decode: \(error)")
         return
       }