Equation with condition

I've gone temporarily dense or something, not seeing this in the User's 
Guide.  I know how to write an equation on a line of its own, for example

      x = y

using
@CenteredNumberedDisplay @Tag {profound123} @Math {x=y}

But how would I add a condition following the equation,  something like

      x = y     for x>0

but of course looking good?

-- 
Daren Scot Wilson
Escondido California