Is an SVG image purely vectorial or can we combine bitmap images into an SVG image ? How about transforms applied on the bitmap images (perspective, mappings, etc.) ?

Is an SVG image purely vectorial or can we combine bitmap images into an SVG image ? How about transforms applied on the bitmap images (perspective, mappings, etc.) ?

Edit: Images may be included in an SVG by link reference. See http://www.w3.org/TR/SVG/struct.html#ImageElement. My question was in fact if bitmap images may be included inside the svg so that the svg image would be self contained. Otherwise, whenever the svg image is displayed the link must be followed and the image downloaded. Apparently .svg files are simply xml files.