Note that the CSS user agent does not alter the document tree during this phase. Steps 2-5 are addressed by the bulk of this specification. Step 6 lies outside the scope of this specification. The canvas is infinite for each dimension of the space, but rendering generally occurs within a finite region of the canvas, established by the user agent according to the target medium. For instance, user agents rendering to a screen generally impose a minimum width and choose an initial width based on the dimensions of the viewport .
User agents rendering to a page generally impose width and height constraints.
Aural user agents may impose limits in audio space, but not in time. Some aspects of the canvas where the document will be rendered. CSS2 user agents will be able to understand CSS1 style sheets. CSS1 user agents will be able to read CSS2 style sheets and discard parts they don't understand. Also, user agents with no CSS support will be able to display style-enhanced documents.