1 files changed, 5 insertions, 0 deletions
diff --git a/lib/book.js b/lib/book.js
index 96ceb06..a95113d 100644
--- a/lib/book.js
+++ b/lib/book.js
@@ -646,6 +646,11 @@ Book.prototype.parentRoot = function() {
 	return this.root;
 };
 
+// Return true if it's a sub-book
+Book.prototype.isSubBook = function() {
+	return !!this.parent;
+};
+
 // Resolve a path in book
 Book.prototype.resolve = function(p) {
     return path.resolve(this.root, p);