Edit in JSFiddle

var draw = SVG('drawing').size(600, 300)

// draw transformed rect
var rect1 = draw.rect(175, 175).move(75, 50).rotate(20).scale(1, 0.5)
var rect2 = draw.rect(175, 175).move(325, 50).rotate(20).scale(1, 0.5)

// draw bbox
var b1 = rect1.rbox()
draw.rect(b1.width, b1.height).addClass('box').move(b1.x, b1.y)
var b2 = rect2.rbox(draw)
draw.rect(b2.width, b2.height).addClass('box').move(b2.x, b2.y)

//labels
var t1 = draw.text('Relative to screen').move(b1.x, 45)
var t2 = draw.text('Relative to drawing').move(b2.x, 45)