Add comments about the un-sanitized URL.

Riot/Modules/Room/Views/URLPreviews/URLPreviewViewData.swift

@@ -18,7 +18,8 @@ import Foundation
 
 @objc
 class URLPreviewViewData: NSObject {
-    /// The URL that's represented by the preview data.
+    /// The URL that's represented by the preview data. This may have been sanitized.
+    /// Note: The original URL, is stored in ``URLPreviewViewModel``.
     let url: URL
     
     /// The OpenGraph site name for the URL.

Riot/Modules/Room/Views/URLPreviews/URLPreviewViewModel.swift

@@ -23,7 +23,8 @@ class URLPreviewViewModel: NSObject, URLPreviewViewModelType {
     // MARK: - Properties
     
     // MARK: Private
-
+    
+    /// The original (un-sanitized) URL to be previewed.
     private let url: URL
     private let session: MXSession
     
@@ -76,6 +77,7 @@ class URLPreviewViewModel: NSObject, URLPreviewViewModelType {
     }
     
     private func openURL() {
+        // Open the original (un-sanitized) URL stored in the view model.
         UIApplication.shared.open(url)
     }