docs: add DataGrid column targeting docs and examples

Update ALTER PAGE documentation across all required locations:
- Skill file (.claude/skills/mendix/alter-page.md)
- MDL Quick Reference (docs/01-project/)
- Reference page (docs-site/src/reference/page/)
- Language page (docs-site/src/language/)
- Examples page (docs-site/src/examples/)
- Doctype test examples (mdl-examples/doctype-tests/)

All show the dotted gridName.columnName syntax for SET, INSERT,
DROP, and REPLACE operations on DataGrid2 columns.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ako

.claude/skills/mendix/alter-page.md

@@ -126,6 +126,30 @@ REPLACE footer1 WITH {
 
 Replaces the target widget with one or more new widgets. The new widgets use the same syntax as `CREATE PAGE`.
 
+### DataGrid Column Operations
+
+DataGrid2 columns are addressable using dotted notation: `gridName.columnName`. The column name is derived from the attribute short name or caption (same as shown by `DESCRIBE PAGE`).
+
+```sql
+-- SET a column property
+SET Caption = 'Product SKU' ON dgProducts.Code
+
+-- DROP a column
+DROP WIDGET dgProducts.OldColumn
+
+-- INSERT a column after an existing one
+INSERT AFTER dgProducts.Price {
+  COLUMN Margin (Attribute: Margin, Caption: 'Margin')
+}
+
+-- REPLACE a column
+REPLACE dgProducts.Description WITH {
+  COLUMN Notes (Attribute: Notes, Caption: 'Notes')
+}
+```
+
+To discover column names, run `DESCRIBE PAGE Module.PageName` and look at the COLUMN names inside the DATAGRID.
+
 ### ADD Variables - Add a Page Variable
 
 ```sql

docs-site/src/examples/alter-page.md

@@ -82,6 +82,31 @@ ALTER PAGE CRM.Customer_Edit {
 };
 ```
 
+## Modify DataGrid Columns
+
+Target columns using dotted notation `gridName.columnName`:
+
+```sql
+-- Add a column
+ALTER PAGE CRM.Customer_List {
+  INSERT AFTER dgCustomers.Email {
+    COLUMN Phone (Attribute: Phone, Caption: 'Phone')
+  }
+};
+
+-- Remove a column
+ALTER PAGE CRM.Customer_List {
+  DROP WIDGET dgCustomers.OldNotes
+};
+
+-- Rename a column header
+ALTER PAGE CRM.Customer_List {
+  SET Caption = 'E-mail Address' ON dgCustomers.Email
+};
+```
+
+Use `DESCRIBE PAGE CRM.Customer_List` to discover column names.
+
 ## Works on Snippets Too
 
 ```sql

docs-site/src/language/alter-page.md

@@ -213,14 +213,32 @@ ALTER PAGE MyModule.Order_Edit {
 };
 ```
 
-### Add a DataGrid Column
+### DataGrid Column Operations
 
-Since DataGrid columns are part of the widget tree, use INSERT to add columns:
+DataGrid2 columns are addressable using dotted notation: `gridName.columnName`. Use `DESCRIBE PAGE` to discover column names (derived from the attribute short name or caption).
 
 ```sql
+-- Add a column after an existing one
 ALTER PAGE MyModule.Customer_Overview {
-  INSERT AFTER colEmail {
-    COLUMN colPhone (Attribute: Phone, Caption: 'Phone')
+  INSERT AFTER dgCustomers.Email {
+    COLUMN Phone (Attribute: Phone, Caption: 'Phone')
+  }
+};
+
+-- Remove a column
+ALTER PAGE MyModule.Customer_Overview {
+  DROP WIDGET dgCustomers.OldColumn
+};
+
+-- Change a column's caption
+ALTER PAGE MyModule.Customer_Overview {
+  SET Caption = 'E-mail Address' ON dgCustomers.Email
+};
+
+-- Replace a column
+ALTER PAGE MyModule.Customer_Overview {
+  REPLACE dgCustomers.Notes WITH {
+    COLUMN Description (Attribute: Description, Caption: 'Description')
   }
 };
 ```

docs-site/src/reference/page/alter-page.md

@@ -76,6 +76,19 @@ Removes one or more widgets by name. The widget and all its children are removed
 
 Replaces a widget (and its entire subtree) with one or more new widgets.
 
+### DataGrid Column Operations
+
+DataGrid2 columns are addressable using dotted notation: `gridName.columnName`. The column name matches the name shown by `DESCRIBE PAGE` (derived from the attribute short name or caption).
+
+All four operations (SET, INSERT, DROP, REPLACE) support dotted column references:
+
+```sql
+SET Caption = 'Product SKU' ON dgProducts.Code
+DROP WIDGET dgProducts.OldColumn
+INSERT AFTER dgProducts.Price { COLUMN Margin (Attribute: Margin) }
+REPLACE dgProducts.Description WITH { COLUMN Notes (Attribute: Notes) }
+```
+
 ### SET Layout
 
 Changes the page's layout without rebuilding the widget tree. Placeholder names are auto-mapped by default. If the new layout has different placeholder names, use `MAP` to specify the mapping.

docs/01-project/MDL_QUICK_REFERENCE.md

@@ -621,6 +621,9 @@ Modify an existing page or snippet's widget tree in-place without full `CREATE O
 | Drop widgets | `DROP WIDGET name1, name2` | Remove widgets by name |
 | Replace widget | `REPLACE widgetName WITH { widgets }` | Replace widget subtree |
 | Pluggable prop | `SET 'showLabel' = false ON cbStatus` | Quoted name for pluggable widgets |
+| Set column prop | `SET Caption = 'New' ON dgGrid.colName` | Dotted ref targets DataGrid column |
+| Drop column | `DROP WIDGET dgGrid.colName` | Remove a DataGrid column |
+| Insert column | `INSERT AFTER dgGrid.colName { COLUMN ... }` | Add column to DataGrid |
 | Add variable | `ADD Variables $name: Type = 'expr'` | Add a page variable |
 | Drop variable | `DROP Variables $name` | Remove a page variable |
 | Set layout | `SET Layout = Module.LayoutName` | Change page layout, auto-maps placeholders |

mdl-examples/doctype-tests/03-page-examples.mdl

@@ -2259,6 +2259,20 @@ ALTER PAGE PgTest.P033b_DataGrid_ColumnProperties {
   SET Layout = Atlas_Core.Atlas_TopBar;
 };
 
+-- MARK: ALTER PAGE DataGrid Column Operations
+
+-- =============================================================================
+-- ALTER PAGE - DataGrid Column Operations (dotted widget references)
+-- =============================================================================
+--
+-- DataGrid2 columns are addressable using gridName.columnName syntax.
+-- Column names are derived from the attribute short name or caption.
+
+-- DROP a column by dotted reference
+ALTER PAGE PgTest.P033b_DataGrid_ColumnProperties {
+  DROP WIDGET dgProducts.Description
+};
+
 -- MARK: Conditional Visibility/Editability and Responsive Widths
 
 -- =============================================================================