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Is the px unit equivalent to user units?

From: Jonathan Watt <jonathan.watt@strath.ac.uk>
Date: Tue, 03 Jan 2006 02:27:57 +0000
Message-ID: <43B9E12D.2050101@strath.ac.uk>
To: www-svg@w3.org

Hi All,

As many of you are probably aware the provision of the SVG specs for omitting 
units on CSS lengths, and the CSS spec's insistence that they are required, has 
resulted in widespread interoperability problems with the release of Firefox 
1.5. I have recommended to people that to avoid these problems they always use 
px units when they would otherwise have omitted units since the two are 
equivalent. Or so I thought, given the sentences: 'One px unit is defined to be 
equal to one user unit. Thus, a length of "5px" is the same as a length of "5".' 
from:

   http://www.w3.org/TR/SVG11/coords.html#Units

But a little further on you find the sentence: 'Note that use of px units or any 
other absolute unit identifiers can cause inconsistent visual results on 
different viewing environments since the size of "1px" may map to a different 
number of user units on different systems'.

How can you reconcile these statements? Is the latter statement a mistake, or is 
there a reason for it? Is the advice I'm giving sound or not?

I'd like to resolve this as soon as possible (especially if the advice I've been 
giving is not sound) given that I get a lot of hits on my authoring doc.

Regards,
Jonathan
Received on Tuesday, 3 January 2006 02:28:34 GMT

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