User blog comment:ChaoticShadow/Introduction to editing with the Source Editor/@comment-1398253-20150814071320

Size sets the width, not the height, and scales it. Using 10x10px would set the image to be 10px by 10px even if the original image isn't square (say, 40px by 60px), thus stretching or squashing the image. I never bother with the second dimension.

"Spacing (spaing=)" - should be spacing=