DOCBOOK: entity imagedata fileref width

<!ENTITY figure '<mediaobject><imageobject><imagedata 
fileref="image-file"/></imageobject></mediaobject>'>

This entity can be included as &figure; in a xml docbook...

but this is unparsed by saxon,

<!ENTITY figure '<mediaobject><imageobject><imagedata fileref="image-file" 
width="75%"/></imageobject></mediaobject>'>

cause I used % in width attrib; how can I solve this?

thnx
Lore