Nadya,

Here's an example of why I don't like making global environemtn changes if it is not absolutely necessary. The highlighted line is your sample code below would result in EXACT not being reset to the original value.

lparameter lcValue && character value to check
local lcOldExact
lcOldExact=set('exact') && Save current settings
set exact on && To perform exact match
if !empty(this.CursorName) and !empty(lcValue) and type('lcValue')='C'
   if seek(lcValue,this.CursorName, 'Code') && Check if it's duplicate
      =messagebox('There is a duplicate! '+lcValue+ ;
                  ' will not be added!',48,'Warning')
      <strong>return .f.</strong>
   endif
endif
set exact &lcOldExact && Restore old settings
return .t.

Here's your same code with my way of doing it;

LPARAMETERS lcValue && character value to check
LOCAL llReturn
llReturn = .T.
IF !EMPTY(this.CursorName) and !EMPTY(lcValue) and VarType(lcValue)='C'
   IF SEEK(PADR(lcValue,LEN(FieldName)),this.CursorName, 'Code') 
      =MessageBox('There is a duplicate! '+lcValue+ ;
                  ' will not be added!',48,'Warning')
      llReturn = .F.
   ENDIF
ENDIF
RETURN llReturn

In this example I have made two changes, one is not chaging SET EXACT at all, but controlling the comparison by padding the lcValue string (this is exactly the same as setting exact on and not padding). The second change is to use a return variable so that there is ONLY ONE return command in the function.