Attribute syntax:

[12] Attribute   ::=   NSAttName Eq AttValue | QName Eq AttValue

examples:

<a xmlns="http://www.w3.org/1999/xhtml" href='http://www.w3.org/1999/xhtml'/>

In the above, the first is a namespace declaration attribute and the second is a regular attribute.

The contents must be in a quoted literal so there are syntax constraints -- see next few slides.