unit Unit1;
interface
uses
 Windows, Messages, SysUtils, Classes, Graphics, Controls,
 Forms, Dialogs, StdCtrls, ComCtrls;
type
 TForm1 = class(TForm)
  Button1: TButton;
  Button2: TButton;
  RichEdit1: TRichEdit;
  procedure RichEdit1KeyPress(Sender: TObject; var Key: Char);
 private
  { Private declarations }
 public
  { Public declarations }
end;
var
 Form1: TForm1;
implementation
{$R *.DFM}
uses
 richedit;
procedure TForm1.RichEdit1KeyPress(Sender: TObject; var Key: Char);
var
 line, col, indent: integer;
 S: string;
begin
 if key = #13 then
 begin
  key := #0;
  with sender as TRichEdit do
  begin
  {figure out line and column position of caret}
  line := PerForm( EM_EXLINEFROMCHAR, 0, SelStart );
  Col := SelStart - Perform( EM_LINEINDEX, line, 0 );
  {get part of current line in front of caret}
  S:= Copy( lines[ line ], 1, col );
  {count blanks and tabs in this string}
  indent := 0;
  while (indent < length( S )) and (S[indent + 1] in [' ', #9]) do
  Inc( indent );
  {insert a linebreak followed by the substring of blanks and tabs}
  SelText := #13#10 + Copy(S, 1, indent);
  end;
 end;
end;
end.