How to return index of the selected tabnotebook page

[AnsBGA]

#I read through the tabnotebook man page but for some #reason can not get it to work.

while { [ .tnb select ] == "page 3" } {
# while page 3 is selected do something
}

# What the corect syntax fo [.tnb select] command to #return the index of selected page.

Thanks,
Nick