Sometimes while using RichEdit you need to get just part of the text from
that control, without setting a selection and using the SelText property.
The code below shows the way to do that :

{overrides wrong TTextRange definition in RichEdit.pas}
  TTextRange = record
                 chrg: TCharRange;
                 lpstrText: PAnsiChar;
               end;
 

function REGetTextRange(RichEdit: TRichEdit; BeginPos, MaxLength: Integer):
string;
{RichEdit - RichEdit control
BeginPos - absolute  index of first char
MaxLength - maximum chars to retrieve}
var
  TextRange: TTextRange;
begin
  if MaxLength>0 then
  begin
     SetLength(Result, MaxLength);
     with TextRange do
     begin
       chrg.cpMin := BeginPos;
       chrg.cpMax := BeginPos+MaxLength;
       lpstrText := PChar(Result);
     end;
     SetLength(Result, SendMessage(RichEdit.Handle, EM_GETTEXTRANGE, 0,
               longint(@TextRange)));
  end
   else Result:='';
end;

This function can be used to extract a word under the current mouse pointer
position:

function RECharIndexByPos(RichEdit: TRichEdit; X, Y: Integer): Integer;
{function returns absolute character position for given cursor coordinates}

var
  P: TPoint;
begin
  P := Point(X, Y);
  Result := SendMessage(RichEdit.Handle, EM_CHARFROMPOS, 0, longint(@P));
end;

function REExtractWordFromPos(RichEdit: TRichEdit;  X,  Y:  Integer): string;
{X, Y - point coordinates in rich edit control }
{returns word , under current cursor position}

var
  BegPos, EndPos: Integer;
begin
   BegPos := RECharIndexByPos(RichEdit, X,  Y);
  if (BegPos < 0)  or
   (SendMessage(RichEdit.Handle,EM_FINDWORDBREAK,WB_CLASSIFY,BegPos) and
                      (WBF_BREAKLINE or WBF_ISWHITE) <> 0 )      then
   begin
      result:='';
      exit;
  end;

   if SendMessage(RichEdit.Handle, EM_FINDWORDBREAK,  WB_CLASSIFY,  BegPos
- 1) and
      (WBF_BREAKLINE or WBF_ISWHITE)  =  0  then
         BegPos  :=  SendMessage(RichEdit.Handle, EM_FINDWORDBREAK,
                                                  WB_MOVEWORDLEFT, BegPos);
  EndPos  :=  SendMessage(RichEdit.Handle, EM_FINDWORDBREAK,
                                           WB_MOVEWORDRIGHT, BegPos);
  Result  :=  TrimRight(REGetTextRange(RichEdit, BegPos, EndPos - BegPos));
end;