Suppose there is a textbox with the field name 'Comments' and you want to show a tooltip on the textbox field whenever user does a mouse over on that field, you can use the drag and drop code editor to define a condition like below upon the 'onFocus' event:

Here are the steps to understand how you can define such a condition:

1. From the left panel, click on the option 'Custom Functions'. Select the third block called 'Setter' and drag it to center of the editor.

2. In the 'Control Name', select 'Comments'.

3. In the next option 'Property Name', select 'Tooltip'.

4. In the next option 'Value', enter the text 'Enter your comments here'.

5. Once done, click 'OK' (at bottom right) to save the changes and exit the code editor, then save / publish the form design as needed. Once the form design is published and executed, the changes will be applicable for the new forms created under the related form type.