@synindex command is nearly the same as the
@syncodeindex command, except that it does not put the
`from' index entries into the
@code font; rather it puts
them in the roman font. Thus, you use
@synindex when you
merge a concept index into a function index.
See section Index Menus and Printing an Index, for information about printing an index at the end of a book or creating an index menu in an Info file.