Minecraft wiki entry for Classic_0.0.23a_01_(remake), associated text: Ability to copy the URL link to give to other players for them to join.
For browsers that do not support WebRTC, the URL link and "Copy" button have been replaced with the "Save level" and "Load level" buttons.
Clicking on any of these buttons will show the text "<html>" instead of the buttons that allowed the player to save or load a level.