// *** before: ***
// a callback was a method pointer: it needed an object, a method with
// exactly the right signature, and it was written far from the call
type
  TCompareEvent = function(const A, B: string): Integer of object;

  TSorter = class
    function ByLength(const A, B: string): Integer;
  end;

function TSorter.ByLength(const A, B: string): Integer;
begin
  Result := Length(A) - Length(B);
end;

// ...
Sort(List, Sorter.ByLength);   // the local context could not be reached

// *** in version 2009: ***
type
  TCompare = reference to function(const A, B: string): Integer;

procedure Sort(const Items: TStrings; const Compare: TCompare);
begin
  // ...
end;

var
  Limit: Integer;
begin
  Limit := 3;

  // the body is written where it is used, and it captures Limit
  Sort(List,
    function(const A, B: string): Integer
    begin
      if Length(A) > Limit then
        Result := 1
      else
        Result := Length(A) - Length(B);
    end);
end;