Set tab order when document is tagged

lib/page.js

@@ -98,13 +98,20 @@ class PDFPage {
     });
 
     // The page dictionary
-    this.dictionary = this.document.ref({
+    const pageDictionary = {
       Type: 'Page',
       Parent: this.document._root.data.Pages,
       MediaBox: [0, 0, this.width, this.height],
       Contents: this.content,
-      Resources: this.resources
-    });
+      Resources: this.resources,
+    };
+
+    // Set tab order if document is tagged for accessibility.
+    if (this.document.getMarkInfoDictionary().data.Marked === true) {
+      pageDictionary.Tabs = 'S';
+    }
+
+    this.dictionary = this.document.ref(pageDictionary);
 
     this.markings = [];
   }

tests/unit/markings.spec.js

@@ -623,6 +623,11 @@ EMC
         `(My Title)`,
         `endobj`
       ]);
+      expect(docData).toContainChunk([
+        `10 0 obj`,
+        /\/Tabs \/S/,
+        `endobj`
+      ]);
     });
   });