Values of attributes can be used as selection criteria. Function normalize-space removes leading and trailing spaces and replaces sequences of whitespace characters by a single space.
//BBB[@id='b1']
Select BBB elements which have attribute id with value b1
<AAA>
<BBB id = "b1"/>
<BBB name = " bbb "/>
<BBB name = "bbb"/>
</AAA>
//BBB[@name='bbb']
Select BBB elements which have attribute name with value 'bbb'
<AAA>
<BBB id = "b1"/>
<BBB name = " bbb "/>
<BBB name = "bbb"/>
</AAA>
//BBB[normalize-space(@name)='bbb']
Select BBB elements which have attribute name with value bbb, leading and trailing spaces are removed before comparison
<AAA>
<BBB id = "b1"/>
<BBB name = " bbb "/>
<BBB name = "bbb"/>
</AAA>