Add properties to HTML Range interface

See:
https://dom.spec.whatwg.org/#range

Sources/HTMLRange.h

@@ -6,8 +6,47 @@
 //  Copyright © 2016 BrainCookie. All rights reserved.
 //
 
-#import <Foundation/Foundation.h>
+#import "HTMLNode.h"
 
+/**
+ A HTML Range, represents a sequence of content within a node tree. 
+ Each range has a start and an end which are boundary points. 
+ A boundary point is a tuple consisting of a node and a non-negative numeric offset.
+
+ https://dom.spec.whatwg.org/#ranges
+ */
 @interface HTMLRange : NSObject
 
+/**
+ The node of the start boundary point.
+ */
+@property (nonatomic, readonly, strong) HTMLNode *startContainer;
+
+/**
+  The offset of the start boundary point.
+ */
+@property (nonatomic, readonly, assign) NSUInteger startOffset;
+
+/**
+ The node of the end boundary point.
+ */
+@property (nonatomic, readonly, strong) HTMLNode *endContainer;
+
+/**
+ The offset of the end boundary point.
+ */
+@property (nonatomic, readonly, assign) NSUInteger endOffset;
+
+/**
+ Checks whether the range is collapsed, i.e. if start is the same as end.
+
+ @return `YES` if the range is collapsed, `NO` otherwise.
+ */
+@property (nonatomic, readonly, assign, getter=isCollapsed) BOOL collapsed;
+
+/**
+ The common container node that contains both start and end nodes.
+ */
+@property (nonatomic, readonly, weak) HTMLNode *commonAncestorContainer;
+
 @end