Re: [svg-developers] explaining setAttribute, setAttributeNS and carburetors

2010-10-17 Thread ddailey 
Jacob, Doug and Wade,

Thanks for your assistance here. It definitely helps!

regards
David
  - Original Message - 
  From: Jacob Beard 
  To: svg-developers 
  Sent: Sunday, October 17, 2010 3:59 AM
  Subject: Re: [svg-developers] explaining setAttribute, setAttributeNS and 
carburetors



  On Sun, Oct 17, 2010 at 6:48 AM, Doug Schepers d...@schepers.cc wrote:

   But in this case, the only thing to know there is that (for whatever
   reason) attributes are generally in the 'null' namespace (*not* in the
   SVG or HTML or whatever host-language namespace). I recommend teaching
   setAttribute for normal attributes, and setAttributeNS only for xlink:href.

  The DOM Level 2 Core spec has something to say about mixing
  namespace-aware DOM methods with non-namespace-aware DOM methods:

  Note: DOM Level 1 methods are namespace ignorant. Therefore, while it
  is safe to use these methods when not dealing with namespaces, using
  them and the new ones at the same time should be avoided. DOM Level 1
  methods solely identify attribute nodes by their nodeName. On the
  contrary, the DOM Level 2 methods related to namespaces, identify
  attribute nodes by their namespaceURI and localName. Because of this
  fundamental difference, mixing both sets of methods can lead to
  unpredictable results. In particular, using setAttributeNS, an element
  may have two attributes (or more) that have the same nodeName, but
  different namespaceURIs. Calling getAttribute with that nodeName could
  then return any of those attributes. The result depends on the
  implementation. Similarly, using setAttributeNode, one can set two
  attributes (or more) that have different nodeNames but the same prefix
  and namespaceURI. In this case getAttributeNodeNS will return either
  attribute, in an implementation dependent manner. The only guarantee
  in such cases is that all methods that access a named item by its
  nodeName will access the same item, and all methods which access a
  node by its URI and local name will access the same node. For
  instance, setAttribute and setAttributeNS affect the node that
  getAttribute and getAttributeNS, respectively, return.
  http://www.w3.org/TR/DOM-Level-2-Core/core.html

  So, it seems like if you're strictly following the spec, mixing
  setAttribute and setAttributeNS might not be the best idea, as it may
  lead to inconsistent results across implementations. In practice, I
  very rarely use the non-namespaced versions (only when I need to do a
  bit of HTML DOM scripting in IE), so this may work just fine.

  Best,

  Jake


  

[Non-text portions of this message have been removed]





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Re: [svg-developers] explaining setAttribute, setAttributeNS and carburetors

2010-10-17 Thread Doug Schepers 
Hi, Jacob-

Jacob Beard wrote (on 10/17/10 3:59 AM):
 Note: DOM Level 1 methods are namespace ignorant. Therefore, while it
 is safe to use these methods when not dealing with namespaces, using
 them and the new ones at the same time should be avoided.

Thanks for digging that up.  I think the author of that may actually 
have been a bit confused... or at least, they didn't state the facts 
clearly.  (There may have been a bit of propagandizing there, as well, 
to get people to use XML namespaces more, perhaps.)

Indeed, if you try to set a namespaced attribute with setAttribute(), it 
won't work correctly... the attribute will be placed in the null 
namespace.  So, when you use

  el.setAttribute( xlink:href, #foo );

it's the equivalent of using

  el.setAttributeNS( null, xlink:href, #foo );

where the local node-name (unintuitively) is 'xlink:href', not 'href' in 
the XLink namespace.

But that's only when you're dealing with namespaces.  Since most 
attributes are in the null namespace, and setAttribute() places 
everything in the null namespace, then these are equivalent and 
perfectly safe:

  el.setAttribute( fill, #f00 );
  el.setAttributeNS( null, fill, #f00 );


As an aside, this is actually a rather poor design, which could have 
been made better if they had simply accounted for hardcoded prefixed to 
be bound to specific namespaces, rather than introducing the arbitrary 
level of abstraction where any namespace could have any prefix string; 
this is made a bit simpler in HTML5, which does define a few hardcoded 
prefixes for namespaces.  Maybe in some future version of XML, XML 
Namespaces, or the like, this can be be expanded beyond HTML.

Regards-
-Doug




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