Trigger event on focus

I have the same issue that Greg and Fiona described. I have users filling out a form onscreen, with a text entry box for each field. Underneath each text entry box I have a text box that describes what information should be entered in each field. When the user clicks on the text entry box, I have a trigger that changes the state of the underlying descriptive text to hidden.

Worked beautifully until a reviewer used the Tab key to go from field to field. The text entry boxes are in focus, but not selected, so the trigger to hide the descriptive text never gets activated. What I need is a trigger that activates when a text entry box GAINS focus, not loses focus. Seems like this would be an important feature to have for accessibility.