[Javascript] See if item is hidden...

[jsWalter]

Anyone have any idea how I can discover if a page item is hidden if it
is a child of some other element?

Example: I have 2 DIV, each DIV has 2 SPANs, each SPAN has 2 Ps,

      DIV a
        SPAN a1
           P  a11
           P  a12
        SPAN a2
           P  a21
           P  a22

      DIV b
        SPAN b1
           P  b11
           P  b12
        SPAN b2
           P  b21
           P  b22

Now, the user turns "off" DIV 'a' and everything it has disappears.

Say I want to insert some text in 'Pa21', but I need to know if it is
showing or not.

How can I know if 'Pa21' is "showing"?

Thanks

Walter