Making a field under a show/hide header mandatory

Problem

If a checkbox with a value of "Other" needs to show a mandatory "Other Description" field when "Other" is selected, and you make the "Other Description" field mandatory (uncheck Allow Empty), the page will not save when that field is left blank, even when it’s under a show/hide header that is only visible when "Other" is selected.

Solution

Where
(a) the checkbox field has n values, of which the "Other" value is the nth, and an HTML tag of onclick="_showhideheadercheckbox(12345,this,'Other');onlyonechecked(this)"
(b) the field to be made mandatory is under a Title Bar with the custom field id of 12345

The field to be made mandatory should have
(c) Allow Empty unchecked and
(d) the following in the JavaScript Validation:

!=''||!document.getElementById('cf_1345342_n-1').checked

So that if "Other" is the 5th value on the checkbox list, n-1 = 4