Can you control Visibility of a Flexfield from the selection of another flexfield?

Summary

Control the visibility of a flexfield based on the result of another flexfield

Content

Is there a way to control the visibility of a flexfield based on the result of another flexfield?

For example, in flexfield A I have a drop down with 5 selections.  One of the selections on that drop down is Other.  In flexfield B I have an open text field for additional information.  When I select Other in flexfield A, I want flexfield B to be visible and mandatory.

I know you have the ability to do it with standard fields but I have not been able to find examples of controlling visibility of a flexfield base on the results of another flexfield.