Fully support accessibility features from PDF reference.

docs/accessibility.md

@@ -15,9 +15,11 @@ This checklist covers everything that is required to create a conformant Tagged
    details).
  * Pass the option `tagged: true` when creating your `PDFDocument` (technically, this sets the
    `Marked` property in the `Markings` dictionary to `true` in the PDF).
+ * Specify natural language in the document options and/or logical structure and/or
+   non-structure marked `Span` content.
  * Add logical structure with all significant content included.
  * Include accessibility information (such as alternative text, actual text, etc.) in the
-   logical structure.
+   logical structure and/or non-structure marked `Span` content.
  * Include all spaces which separate words/sentences/etc. in your marked structure content,
    even at the ends of lines, paragraphs, etc.. I.e. don't do `doc.text("Hello, world!")` but
    instead do `doc.text("Hello, world! ")`.
@@ -53,6 +55,17 @@ When marking content, you can provide options (take care to use correct capitali
    coordinates
  * `attached` - used for `Pagination` artifact content, array of one or more strings:
    `Top`, `Bottom`, `Left`, `Right`
+ * `lang` - used for `Span` content: human language code (e.g. `en-AU`) which overrides default
+   document language, and any enclosing structure element language
+ * `alt` - used for `Span` content: alternative text for an image or other visual content
+ * `expanded` - used for `Span` content: the expanded form of an abbreviation or acronym
+ * `actual` - used for `Span` content: the actual text the content represents (e.g. if it is
+   rendered as vector graphics)
+
+It is advisable not to use `Span` content for specifying alternative text, expanded form, or
+actual text, especially if there is a possibility of the content automatically wrapping, which
+would result in the text appearing twice. Set these options on an associated structure element
+instead.
 
 ## Logical Structure
 

lib/document.js

@@ -74,6 +74,10 @@ class PDFDocument extends stream.Readable {
       Names
     });
 
+    if (this.options.lang) {
+      this._root.data.Lang = new String(this.options.lang);
+    }
+
     // The current page
     this.page = null;
 

lib/mixins/markings.js

@@ -57,6 +57,20 @@ export default {
         dictionary.Attached = options.attached;
       }
     }
+    if (tag === 'Span') {
+      if (options.lang) {
+        dictionary.Lang = new String(options.lang);
+      }
+      if (options.alt) {
+        dictionary.Alt = new String(options.alt);
+      }
+      if (options.expanded) {
+        dictionary.E = new String(options.expanded);
+      }
+      if (options.actual) {
+        dictionary.ActualText = new String(options.actual);
+      }
+    }
 
     this.addContent(`/${tag} ${PDFObject.convert(dictionary)} BDC`);
     return this;

tests/unit/markings.spec.js

@@ -91,6 +91,13 @@ EMC
 /Attached [/Top]
 >> BDC
 EMC
+/Span <<
+/Lang (en-AU)
+/Alt (Hi, earth! )
+/E (Greetings, terrestrial sphere! )
+/ActualText (Hello, world! )
+>> BDC
+EMC
 `,
         'binary'
       );
@@ -101,6 +108,13 @@ EMC
         attached: [ "Top" ]
       });
       document.endMarkedContent();
+      document.markContent("Span", {
+        lang: "en-AU",
+        alt: "Hi, earth! ",
+        actual: "Hello, world! ",
+        expanded: "Greetings, terrestrial sphere! "
+      });
+      document.endMarkedContent();
       document.end();
 
       expect(docData).toContainChunk([
@@ -447,18 +461,24 @@ EMC
       ]);
     });
 
-    test('identified as tagged', () => {
+    test('identified as accessible', () => {
       document = new PDFDocument({
         info: { CreationDate: new Date(Date.UTC(2018, 1, 1)) },
         compress: false,
         pdfVersion: '1.5',
-        tagged: true
+        tagged: true,
+        lang: 'en-AU'
       });
 
       const docData = logData(document);
 
       document.end();
 
+      expect(docData).toContainChunk([
+        `3 0 obj`,
+        /\/Lang \(en-AU\)/,
+        `endobj`
+      ]);
       expect(docData).toContainChunk([
         `3 0 obj`,
         /\/Markings 5 0 R/,