HTML print with absolute postitions

Question

Is it possible to print a HTML page with truly absolute positioned elements to paper? It seems all browsers are doing a big mess here. It is easy to define a body by absolute units (eg. cm) and place elements by position: absolute inside. However, every browser seem to try to make it impossible to print such a page. FF for example is adding print margins, even when printing to a PDF on linux despite 0-margin page settings. Chrome seems to shrink the page in every case. So how to print something with absolute positioning, eg. paper form fields, markings etc.? Have I overlooked something?

Answer 1

Sadly, the CSS3 Module: Paged Media allows all this to happen. This are the rules concerning pages which are too big:

3.3.3. Rendering page boxes that do not fit a page sheet

If a page box does not match the target page sheet dimensions, the user agent MAY choose (in order of preference) to:

• Render the page box at the indicated size on a larger page sheet.
• Rotate the page box 90° if this will make the page box fit the page sheet.
• Scale the page box to fit the page sheet. (There is no requirement to maintain the aspect ratio of the page or of any elements on the page when scaling; however, preservation of the aspect ratio is preferred.) [done by Chrome]
• Reformat the page contents, including 'spilling' onto other page sheets. [done by many other or older browsers]
• Clip overflowed content (least preferred).

The user agent should consult the user before performing these operations.

3.3.4. Positioning the page box on the sheet

When the page box is smaller than the page size, the user agent should center the page box on the sheet since this will align double-sided pages and avoid accidental loss of information that is printed near the edge of the sheet.

And this is the rule which breaks all your positioned stuff:

3.7. Content outside the page box

[...] Also, when boxes are positioned absolutely, they MAY end up in "inconvenient" locations. For example, images MAY be placed on the edge of the page box. Similarly when boxes use fixed or relative positioning, they MAY also end up outside of the page box.

A specification for the exact formatting of such elements lies outside the scope of this document. However, we recommend that authors and user agents observe the following general principles concerning content outside the page box:

• User agents SHOULD avoid generating a large number of empty page boxes to honor the positioning of elements (e.g., you don't want to print 100 blank pages). Note, however, that generating a small number of empty page boxes MAY be necessary to honor the 'left' and 'right' values for 'page-break-before' and 'page-break-after'.
• Authors SHOULD not position elements in inconvenient locations just to avoid rendering them. Instead:
  • To suppress box generation entirely, set the 'display' property to 'none'.
  • To make a box invisible, set the 'visibility' property.
• User agents MAY handle boxes positioned outside the page box in several ways, including discarding them or creating page boxes for them at the end of the document.

Have a look at the second paragraph of section 3.7: A specification for the exact formatting of such elements lies outside the scope of this document. Since there is no other document and no other guideline then the general principle following this paragraph, every browser can do whatever it want.

It's one of the flaws that are currently in this CSS3 module. However, I think those flaws cannot be removed by a CSS4 or revised CSS3 module, as the variety of possible stylesheets and resulting layouts is too huge too cover. Also note a little footnote given in CSS Print Profile:

‡ The printer MAY ignore positioned elements that are placed on the page before the position of the current element in the normal flow.

So it's basically not possible to create the same effect in every browser. As for the time being, the only possible way to achieve a portable document is to create a PDF with a third-party application or via a PDF printer and your most favorite browser. Every other way is bound to fail as long as either the W3C's recommendations aren't strict or the browser vendors implement whatever they want.

See also:

• CSS3 Module: Paged Media (Working draft, last revision 2006)
• CSS Print Profile (Working draft, last revision 2006)

Additional notes

If you have a bunch of position:absolute elements which need to be printed it's sometimes a good question whether an element actually needs to be positioned absolute, or if the same effect can be achieved in a slightly different or easier way. Also note that you should use display:none on each element that isn't truly needed for the printed media, such as ads, navigations, etc...

Answer 2

As you say, web browsers tend to do crazy things when printing. Print-oriented engines are often better.

WeasyPrint is an open-source engine that renders to PDF and supports absolute positioning as well as CSS 3 Paged Media to set the page margins:

@page { margin: 1cm /* or 0, if you want */ }