### @diffs doesn't seem to work in tutorials

The command "### @diffs true" invariably seems to generate the error message "Unknown command: @diffs" when used as described in the documentation. Starting a document like this, for instance, will generate the error message:

@activities true

@diffs true

scene.setBackgroundColor(9)
let mySprite = sprites.create(img`
    . . . . . . . . . . . . . . . . 
    . . . . . . . . . . . . . . . . 
    . . . . . . . . . b 5 5 b . . . 
    . . . . . . b b b b b b . . . . 
    . . . . . b b 5 5 5 5 5 b . . . 
    . b b b b b 5 5 5 5 5 5 5 b . . 
    . b d 5 b 5 5 5 5 5 5 5 5 b . . 
    . . b 5 5 b 5 d 1 f 5 d 4 f . . 
    . . b d 5 5 b 1 f f 5 4 4 c . . 
    b b d b 5 5 5 d f b 4 4 4 4 b . 
    b d d c d 5 5 b 5 4 4 4 4 4 4 b 
    c d d d c c b 5 5 5 5 5 5 5 b . 
    c b d d d d d 5 5 5 5 5 5 5 b . 
    . c d d d d d d 5 5 5 5 5 d b . 
    . . c b d d d d d 5 5 5 b b . . 
    . . . c c c c c c c c b b . . . 
    `, SpriteKind.Player)
controller.moveSprite(mySprite)# tutorial

So far, I haven't found a working example of @diffs in any code I've browsed through on GitHub.

Using "// @highlight" within the code on the line above the block you need to highlight works as described in the documentation for highighting blocks, but is there a way to highlight variables that's been changed or added within blocks?