Added a some docs and crave-out for relative dates

gspread/worksheet.py

@@ -34,6 +34,7 @@
 from .urls import WORKSHEET_DRIVE_URL
 from .utils import (
     DateTimeOption,
+    RelativeDate,
     Dimension,
     GridRangeType,
     InsertDataOption,
@@ -3203,17 +3204,32 @@ def cut_range(
 
     def add_validation(
         self,
-        range: str,
+        source: str,
         condition_type: ValidationConditionType,
-        *values,
+        *values: Iterable[Any | RelativeDate],
         **kwargs,
     ) -> Any:
-        """
-        Adds a data validation to any given ranges.
+        """Adds a data validation rule to any given range.
+
+        .. note::
+
+            ``condition_type`` values are explained here: `ConditionType`_
+
+            .._ConditionType: https://developers.google.com/sheets/api/reference/rest/v4/spreadsheets/other#ConditionType
+
+        .. note::
+
+            ``RealtiveDate`` values are explained here: ``_
+
+            .._RelativeDate: https://developers.google.com/sheets/api/reference/rest/v4/spreadsheets/other#RelativeDate
+
+        :param str source: The A1 notation of the source range to move
+        :param condition_type: The sort of condition to apply.
+        :param values: List of condition values or RelativeDate.
 
 
         """
-        grid = a1_range_to_grid_range(range, self.id)
+        grid = a1_range_to_grid_range(source, self.id)
 
         body = {
             "requests": [
@@ -3224,14 +3240,19 @@ def add_validation(
                             "condition": {
                                 "type": condition_type,
                                 "values": [
-                                    {"userEnteredValue": value} for value in values
+                                    (
+                                        {"userEnteredValue": value}
+                                        if not isinstance(value, RelativeDate)
+                                        else {"relativeDate": value}
+                                    )
+                                    for value in values
                                 ],
                             }
                         },
-                        **kwargs
+                        **kwargs,
                     }
                 }
             ],
         }
 
-        self.client.batch_update(self.spreadsheet_id, body)
+        self.client.batch_update(self.spreadsheet_id, body)