[TRINIDAD] How to display "Page loading..." while page is loading?

I have an action that takes a few seconds to complete.  I would like the
user to see something link "Page loading..." while the action is
processing.  The action loads a List from a series of database queries
and the page simply displays the list in a table.  Looking at the
examples, it appears that <tr:statusIndicator"> is part of the answer.

My question is how should I do this?

Paul Spencer