For example, in this section
The pipeline style does all the work up front in a standard CGI or mod_perl handler, then decides which template to run and passes some data to it. The template has no control flow logic in it, just presentation logic, e.g. show this graphic if this item is on sale.
now, by 'control flow logic' you certainly mean application control flow. because tt (a pipeline system) certainly has control flow constructs within it. but you will never see tt controllling application flow.