domish.Element checking __class__, breaks inheritance

[VislabSteve]

twisted.xish.domish.Element.addChild checks the class type for setting the parent:
    if node.__class__ == Element:
            node.parent = self
However this breaks when node is a subclass of Element (i.e. inherits from it).
 isinstance(node, Element) would be a better method.

Note there are other places that make this comparison: firstChildElement() and
__getattr__()

Thanks

[ralphm]

Confirmed. It would be even better if we worked with interfaces here, so that we
can avoid the isinstance horrors. I'll look into this.

[ralphm]

source:branches/domish-namespaces-1444-2 adds a domish.IElement to remedy this. When that branch has been merged I'll review the rest of the code to use it.

[ralphm]

As #1444 has been solved, all that remained was replacing isinstance calls. Created source:branches/xish-IElement-1074 and did that.

[warner]

looks good to me, handing back to ralphm for committing

[ralphm]

(In [16693]) Remove last occurance of isinstance on Element objects

Author: ralphm Reviewer: warner Fixes #1074

[radix]

Milestone Twisted-2.3 deleted