in packages/svg-mixer/lib/image.js [18:30]
get viewBox() {
const { width, height } = this;
const { viewBox } = this._tree.root.attrs || {};
let result;
if (viewBox) {
result = viewBox.split(' ').map(parseFloat);
} else if (width && height) {
result = [0, 0, width, height];
}
return result;
}