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[css2] Added page information, viewport information, and new canvas information
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‎css2/conform.src‎

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<html lang="en">
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<!-- $Id: conform.src,v 1.13 1997-09-23 14:10:07 ian Exp $ -->
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<!-- $Id: conform.src,v 1.14 1997-10-01 22:16:51 ian Exp $ -->
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<HEAD>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<TITLE>Definitions and document conventions</TITLE>
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<P>User agents that don't actually use style sheets to specify default
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rules must behave as if they did.
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<H3><<span class="index-def" title="flow model">flow model</span></H3>
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The <a href="./flowobj.html">visual flow model</a> describes how user
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agents should format a stream of elements.
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<H3><span class="index-def" title="canvas">Canvas</span></H3>
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<!-- Hakon: introduce notion of "viewport"? -->
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<P> The canvas is the part of a visual user agent's drawing surface onto which
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documents are rendered. No structural element of a document
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corresponds to the canvas.
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<P>The dimensions of the canvas (which affect <a
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href="./flowobj.html">visual formatting</a>) are set by the user
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agent. The user agent may change the dimensions of the canvas when the
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viewing area is resized.
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<P>When a document doesn't cover the entire canvas, user agents should
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display the background according to the following algorithm (which
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derives from HTML precedent): if the <span
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class="propinst-background">'background'</span> value of the HTML
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element is different from 'transparent' then use it, else use the
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<P> The canvas is the part of a visual user agent's drawing surface
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onto which documents are rendered. Users see the canvas through a user
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agent's <span class="index-def"
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title="viewport"><em>viewport</em></span>, a window or other viewing
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area on the screen. The canvas may be larger or smaller than the
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viewport. Typically, when the canvas is larger than the viewport, the
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user agent will offer the user a scrolling mechanism to bring hidden
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parts into view.
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<P>The canvas is generally as long as the document flowed onto it, but
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has a fixed width, set by the user agent. The width affects formatting
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according to the <a href="./flowobj.html#visual-flow">visual flow
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model</a> The user agent may change the dimensions of the canvas when
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the viewport is resized.
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<P>When an HTML document doesn't cover the entire canvas, user agents
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should display the background according to the following algorithm: if
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the <span class="propinst-background">'background'</span> value of the
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HTML element is different from 'transparent' then use it, else use the
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<span class="propinst-background">'background'</span> value of the
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BODY element. If the resulting value is 'transparent', the rendering
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is undefined.
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fully cover the canvas) will be red.
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</div>
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<P>In HTML, until other means of addressing the canvas become
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available, we recommend that canvas properties be set on the BODY
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<P>Note that no structural element of a document corresponds to the
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canvas. In HTML, until other means of addressing the canvas become
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available, we recommend that authors set canvas properties on the BODY
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element.
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<H3><a name="page">The page</a></H3>
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<P>In order to handle paged media (printing, slides, etc.) correctly,
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we introduce the notion of the <span class="index-def"
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title="page"><em>page</em></span>, which is like a canvas except that
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both its width and height are finite. In the section on <a
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href="./print.html#page-breaks">page breaks</a>, we discuss how user
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agents must adapt the <a href="flowobj.html#flow-model">visual flow
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model</a> to the case of paged media.
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<P>That a "page" is an abstract rectangle that may or may not
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correspond to the size of a physical "sheet" of paper, transparency,
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etc. Once a page has been formatted, it is the user agent's
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responsibility to transfer pages to paper. The transfer may vary in
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complexity. Some transfer possibilities include:
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<ul>
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<li>One page to one sheet of paper.
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<li>Two pages to one sheet of paper (double-sided printing).
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<li>N (small) pages to one sheet of paper (called <span
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class="index-def" title="n-up"><em>n-up</em></span>
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printing).
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<li>One (large) page to N x M sheets of paper (called "tiling").
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<li>Signatures (a group of pages
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printed on a sheet, which, when folded and trimmed like a book, appear in their
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proper sequence).
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<li>Printing to alternate paper trays.
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<li>Printing to a file.
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</ul>
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<P>The transfer mechanism from page to sheet lies beyond the scope of
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this specification. However, the user agent does need to target
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a certain size and orientation when printing, and this is known as the
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<span class="index-def" title="print target"><EM>print
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target</EM></span>. The user will typically set set the target size
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and orientation in the <EM>Print</EM> dialogue box of the UA. There
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will often, but not always, be a correlation between the target size
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and the sheet size.
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<H2>Conventions</H2>
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<H3><a name="property-defs">CSS property definitions</a></H3>
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<P>Each CSS property definition begins with a summary of key

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