They may appear in any order. Attribute names are always case-insensitive.
Attribute values are generally case-insensitive.
If no abbreviation is listed, the default abbreviation is the cell content. All cell contents will be displayed over this image. If the referenced image is smaller than the table cell size, it will be tiled to fit all of the cell area. The value for this attribute indicates the URL to reference the graphic. The standard HTML color specification methods.