Invoked when the user tries to enter a character in a cell of a control that allows editing of text (such as a text field or form field).
- macOS 10.0+
The control whose content is about to be edited.
The field editor of the control.
YES if the control's field editor should be allowed to start editing the text; otherwise,
You can use this method to allow or disallow editing in a control. This message is sent by the control directly to its delegate object.