From Xojo Documentation
The zero-based way to lookup controls in the window.
All controls on the window are returned as a the Control base type. You can use the IsA operator to check the specific type to see if the control is a PushButton, Label, etc.
This example is in the Action event of a PushButton and displays the name of the first control in Window:
Loop through all the controls on a Window and disable only the TextFields: