%inside-chem-struct-wrap.class;
Inside Chemical Structure Elements
Very similar to the Simple Display Class Elements, but for use inside <chem-struct-wrap>, so it can contain both <chem-struct> and <textual-form> 
Model
<!ENTITY % inside-chem-struct-wrap.class
                        "alternatives | chem-struct | code | graphic |
                         media | preformat | textual-form"           >