If you include just the height keyword or just the width keyword, the other dimension is adjusted automatically to prevent the image from stretching. It's only when I include both the height and the width that it becomes subject to stretching (if I don't make sure my height and width lengths are congruent to the original lengths).
Plus, if I understand correctly how the browser renders the the HTML and style sheets (disclosure: most of my career is back-end data programming, not making front end screens), having just one dimension listed in the img tag helps the browser make automatic adjustments for things like users having various screen sizes, or if the user shrinks or enlarges his browser window, or a phone user turns it sideways. IIRC, the browser can make those kinds of adjustments easier and still have a nice style if we tell it the length of just one dimension and not both dimensions.
Plus, if I understand correctly how the browser renders the the HTML and style sheets (disclosure: most of my career is back-end data programming, not making front end screens), having just one dimension listed in the img tag helps the browser make automatic adjustments for things like users having various screen sizes, or if the user shrinks or enlarges his browser window, or a phone user turns it sideways. IIRC, the browser can make those kinds of adjustments easier and still have a nice style if we tell it the length of just one dimension and not both dimensions.
Aha, mystery solved, Thx.