Re: [xml] Questions about xml:id

[Rob Richards <rrichards ctindustries net>]

Funny this topic came up as I just recently was looking at the id stuff 
for the PHP DOM extension. Have a few questions/comments as well as a 
few issues regarding this.

Daniel Veillard wrote:

> > It seems that libxml2 only gives an attribute that magic ID-ness
> > if the attribute's local-name is "xml:id"
> > [in perl:  $node->setAttribute('xml:id','someid'); ]
> > rather than an "id" attribute in xml namespace
> > [in perl: 
> > $node->setAttributeNS('http://www.w3.org/XML/1998/namespace','id','someid'); ]
> > Is this the intention?
> >    
>
>  Well the focus so far has mostly been toward parsing xml:id and handling
> it only from a serialization. I didn't really looked at it from an API
> perspective. But the behaviour exposed sounds like a bug.
>  
Should the ID really be set with setAttribute/NS functions or should it 
only be only set (when manually building a tree that is) using one of 
the setIdAttribute methods from core 3 - meaning it would be up to the 
developer to call xmlAddID?

>  it's not complete probably. Removal of the attribute generate removal
> from the ID table, but modification are not tracked down apparently.
> Sounds like a bug too.
>  
This is where I started running into issues. both xmlIsID and 
xmlFreeProp only handle IDs if the doc has intSubset or extSubset. Using 
xml:id or implementing setIdAttribute does not require subsets, so if 
the attribute gets freed along the way, the ID never gets removed from 
the table and calling xmlGetID returns invalid data.

I can understand wanting to do that type of check as to not have to 
check every attribute when being free for performance reasons, so was 
wondering wether the attribute atype could also be added so that either 
the doc has a subset or atype==XML_ATTRIBUTE_ID. This would also require 
resetting the atype in xmlRemoveID as it gets set in xmlAddID but never 
reset when removed.

Next in xmlFreeProp is the check for attribute parent. The attribute 
itself can get unlinked and freed but xmlFreeProp only checks for an ID 
if the attribute has a parent. I'm not sure wether the the attribute 
remains and ID if unlinked, but if it doesn't, then xmlUnlinkNode should 
remove the ID. If it still remains an ID then xmlFreeProp should not 
require a parent node when checking if attribute is an ID to be removed.

Rob