In tables, the horizontal dimensions of a column.
On Image Data, this attribute is used to control the size of the image in display.
In keeping with Docbook, this attribute designates the width of an image (or table cells) in the rendering device (the browser), expressed either as an absolute size (in pixels) or relatively, as a percentage of available space.
When this attribute is not provided, an image will be displayed at its native resolution. Only larger images (more than about 800 pixels wide) need to be scaled down using this attribute. It is recommended that percentage values be given.