use.role.for.mediaobject — Use role attribute value for selecting which of several objects within a mediaobject to use.
The order of selection when then parameter is non-zero is:
If the stylesheet parameter preferred.mediaobject.role has a value, then the object whose role equals that value is selected.
Else if an object's role attribute has a value of html for HTML processing or fo for FO output, then the first of such objects is selected.
Else the first suitable object is selected.
If the value of use.role.for.mediaobject is zero, then role attributes are not considered and the first suitable object with or without a role value is used.