[newbie] ratsimp question



Consider for example the expression 
expr:x^g(x^(b+1/b)); 

How to ratsimp subexpression b+1/b ? 
I tried 
ratsimp(expr), ratsimpexpons:true

but don't work (I expect something as x^g(x^((b^2+1)/b)))  )

For  simple example expr: g(x^(b+1/b)) 
rat(expr), ratsimpexpons:true  
work as expected  but  not ratsimp(expr), ratsimpexpons:true (why?)