Attributes in default namespace behave oddly

[IMSoP]

There seems to be a bug (or misfeature?) in SimpleXML where attributes in the default namespace don't show if you call ->attributes($default_namespace_uri) rather than ->attributes('', true).

Because of simplexml_dump's attempts to display namespace information, this leads to data disappearing from view with innocuous XML like this:

<?php
include 'simplexml_dump.php';

$xml = <<<XML
<?xml version="1.0"?>
<Foo xmlns="http://example.com">
        <Bob InvisibleAttribute="You ain't seen me, right?">
                <MaskingChildElement />
        </Bob>
</Foo>
XML;

$sx_Foo = simplexml_load_string($xml);
simplexml_dump($sx_Foo->Bob);

[IMSoP]

A bit of research shows this may actually be correct behaviour, if not exactly user-friendly: an attribute with no qualifier is technically in no namespace at all, even if a default namespace was declared.

See e.g. http://stackoverflow.com/questions/10672635/xml-namespaces-and-unprefixed-attributes for discussion of this slightly baffling area of XML namespace logic...

[IMSoP]

Also need to work out how this affects simplexml_tree: if we suggest that the full URI is used for all calls to ->children() (see #5) then calls to such "namespaceless attributes" will have to be expressed as ->attributes()->foo rather than ['foo'].