@synindex: Combining indices
@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 Printing Indices & Menus, for information about printing an index at the end of a book or creating an index menu in an Info file.