2.1.2 [SVG11] Section 7.7, The viewBox attribute
The specification states:
All elements that establish a new viewport (see elements that establish viewports), plus the 'marker', 'pattern' and 'view' elements have attribute viewBox. The value of the viewBox attribute is a list of four numbers <min-x>, <min-y>, <width> and <height>, separated by whitespace and/or a comma, which specify a rectangle in user space which should be mapped to the bounds of the viewport established by the given element, taking into account attribute preserveAspectRatio. If specified, an additional transformation is applied to all descendants of the given element to achieve the specified effect. A negative value for <width> or <height> is an error (see Error processing). A value of zero disables rendering of the element.
IE9 Mode, IE10 Mode, IE11 Mode and Edge (beta) Mode (All Versions)
A value of 0 on the viewBox height or width does not disable rendering of the element.