BITS 0.2
( ( object-id )*, label?, ( caption )?, ( alt-text | long-desc | email | ext-link
| uri )*, ( alternatives | chem-struct | graphic | media | preformat | textual-form
)+, ( attrib | permissions )* )
BITS 1.0
( ( object-id )*, label?, ( caption )?, ( abstract )*, ( kwd-group )*, ( alt-text
| long-desc | email | ext-link | uri )*, ( alternatives | chem-struct | code | graphic
| media | preformat | textual-form )+, ( attrib | permissions )* )
BITS 2.0
NO CHANGE IN CONTENT MODEL
BITS 2.1
( ( object-id )*, label?, ( caption )?, ( legend )*, ( abstract )*, ( kwd-group )*,
( subj-group )*, ( alt-text | long-desc | email | ext-link | uri )*, ( alternatives
| chem-struct | code | graphic | media | preformat | textual-form )+, ( attrib | permissions
)* )