Add property depth to article and pages

lib/backbone/summary.js

@@ -74,6 +74,7 @@ TOCArticle.prototype.getContext = function() {
     return {
         level: this.level,
         title: this.title,
+        depth: this.depth(),
         path: this.isExternal()? undefined : this.path,
         anchor: this.isExternal()? undefined : this.anchor,
         url: this.isExternal()? this.ref : undefined
@@ -105,6 +106,11 @@ TOCArticle.prototype.hasParent = function() {
     return !(this.parent instanceof TOCPart);
 };
 
+// Return depth of this article
+TOCArticle.prototype.depth = function() {
+    return this.level.split('.').length;
+};
+
 // Return next article in the TOC
 TOCArticle.prototype.next = function() {
     return this._next;

lib/page/index.js

@@ -122,6 +122,7 @@ Page.prototype.getContext = function() {
                 next: next? next.getContext() : null,
                 previous: prev? prev.getContext() : null,
                 level: article? article.level : null,
+                depth: article? article.depth : 0,
                 content: this.content,
                 dir: dir
             }

test/summary.js

@@ -105,6 +105,12 @@ describe('Summary / Table of contents', function() {
             book.summary.getArticleByLevel('2.1').title.should.equal('Hello 3');
             book.summary.getArticleByLevel('2.1.1').title.should.equal('Hello 4');
         });
+
+        it('should correctly calcul depth', function() {
+            book.summary.getArticleByLevel('0').depth().should.equal(1);
+            book.summary.getArticleByLevel('1.1').depth().should.equal(2);
+            book.summary.getArticleByLevel('1.1.1').depth().should.equal(3);
+        });
     });
 
     describe('External', function() {