Q:

What is the validation syntax to require a value to be selected? 

I have been using the visible validation attribute in Orbeon Forms with this syntax:  
$control-132 = 'yes'

Basically, the yes means that the control's radio button labeled 'yes' has been selected. If a user selects the 'yes' radio button, a hidden control with the validation becomes visible. Can anyone tell me how to write an expression that simply validates data has been entered in a field?
IE- I tried to write  --- $control-132 = 'yes' --- be written --- $control-132 = '*'--- 
Didn't work.
I just need the validation to occur if ANY data had been entered into the control. 

A:

I gather that you want to make the field invalid if users forget to select one of the options you provided, in this case through radio buttons. If this is indeed the case, you can just mark the field as required. (If using Form Builder, you have a "Required" radio button you can set to "Yes". If you're writing XForms, using <xforms:bind required="true()"/>.
Alternatively, if you really want to do this with an XPath expression, the expression would be: $my-field != ''.

