Add height and width in image in exercises; quotes necessary?

When adding an image you can set height and width, without using single or double quotation marks on the edges.

img src=“” class=“img-responsive” alt="Three kittens running towards the camera. " height=“102” width=102

Notice how at the end the ‘102’ is without quotations.
In the code editor it seems to run both with, or without quotes.

Is it mandatory to add (single or double) quotation marks for a number?