If you have an element like

<name attribute=value attribute="value" attribute='value'>

this regex could be used to find successively each attribute name and value

(\S+)=["']?((?:.(?!["']?\s+(?:\S+)=|[>"']))+.)["']?

Applied on:

<a href=test.html class=xyz>
<a href="test.html" class="xyz">
<a href='test.html' class="xyz">

it would yield:

'href' => 'test.html'
'class' => 'xyz'