s an attribute it does not
recognize, it must ignore the entire attribute specification
(i.e., the attribute and its value).</li>

<li>If a user agent encounters an attribute value it doesn't
recognize, it must use the default attribute value.</li>

<li>If it encounters an entity reference (other than one
of the predefined entities) for which the User Agent has 
processed no declaration (which could happen if the declaration
is in the external subset which the User Agent hasn't read), the entity 
reference 