establishing a new viewport

Hi,

1.        Section 7.6 Establishing a New Viewport: the <svg> .... mentions:
To establish a new viewport, you use the positioning properties from CSS
such as ‘left’, ‘top’, ...
Does this imply that it is the only way we do it ?
or, May we still use the x=, y=, width=, height= attributes for establishing
a new viewport ?

2.        If I include an <svg> element inside an SVG document such as:
<svg width=”500” height=”500” viewBox=”0 0 1000 1000”>
        <desc> This SVG drawing embeds another one, thus establishing a new
viewport
        </desc>

         <svg style=”left: 50%; top: 25%” width=”100%” height=”100%”>
        <!-- drawing B goes here -->
         </svg>
</svg>
Will the new viewport’s size be determined relatively to the viewBox space
or the viewport space of the parent <svg> element ?
Does the answer to this question still apply if I use the x=, y=, width=,
height= attributes for establishing the new viewport ?

Thank you so much.
Jojada.-