doc: Add notes to 'end' docstring about class and subsref limation (b…

…ug #59737)

* libinterp/parse-tree-pt-eval.cc (end):  Add programming note indicating
that end cannot be used in subsref, subsasgn, substruct for indexing. Add
second note describing how end must be overloaded for use in indexing with
classes.

libinterp/parse-tree/pt-eval.cc

@@ -2280,6 +2280,31 @@ last valid entry in an indexing operation.
  @result{} 6
 @end group
 @end example
+
+Programming notes:
+@enumerate
+@item
+The @code{end} keyword cannot be used within @code{subsref},
+@code{subsasgn}, or @code{substruct} for manual indexing operations.
+
+@item
+For custom classes, to enable use of @code{end} in indexing expressions it
+must be overloaded with a function definition such as:
+   @example
+   @group
+   function last_index = end (obj, end_dim, ndim_obj)
+     if (end_dim == ndim_obj)
+       last_index = prod (size (obj)(end_dim:ndim_obj));
+     else
+       last_index = size (obj, end_dim);
+     endif
+   endfunction
+   @end group
+   @end example
+For more information see
+@ref{Object Oriented Programming, , Object Oriented Programming}.
+@end enumerate
+
 @seealso{for, parfor, if, do, while, function, switch, try, unwind_protect}
 @end deftypefn */)
 {