styles system and overrides

To solve this situation, a list of "overrides" can be defined, with element definitions to be overridden. Each element in the list is much similar to a normal element definition, with the exception that attributes and styles can be set to "null" to catch all values, or a regular expression.

<Style name="class1" element="span">
<Attribute name="class" value="class1" />
<Override name="class" value="class2" />
</Style>

<Style name="class2" element="span">
<Attribute name="class" value="class2" />
<Override name="class" value="class1" />
</Style>