Navigator 2.0, Internet Explorer 3.0
The onfocus() event handler of a form element is invoked by the web browser when the user transfers the keyboard focus to that element. Note that it is not invoked when focus is programmatically transfered with the focus() method.
The onfocus() event handler is available for all form elements except the Hidden element. For Navigator 2.0 and 3.0 on Unix platforms, however, it is only invoked for the text-entry elements: Text, Textarea, Password and FileUpload. Note that in Navigator 3.0, the Window object also defines an onfocus() event handler.