Sometimes you may want to write a single page on something but expect
to expand it to a set of pages later on.
don't want to have to
change your URL
There is a special feature to simplify this: if a directory contains
just the index.html file and an empty
sidebar.txt file then the sidebar generated for this directory is
exactly the same as if this was a single file in the directory above
set of tabbed pages
is an example of this - the URL points to a directory but
it appears in the sidebar as if it were just a file in the parent directory.