M = moveto
L = lineto
H = horizontal lineto
V = vertical lineto
C = curveto
S = smooth curveto
Q = quadratic Bezier curve (A Bezier curve with one control point)
T = smooth quadratic Bezier curveto
A = elliptical Arc
Z = closepath
The shadow is the alpha channel of the square
The shadow is the square which is blurred and has color changed.
The SVG element is used to embed bitmap images inside your SVG image. This way you can draw ontop of, or next to, the bitmap image. And/or use filters on them.