How can you script in the *.ss files?

What scripting language does silverstripe use.
I thought it was php but I can't get php to
work in the *.ss files.

I tried
<% ... %>
and
<?php ?> works only for /* */ comments
// comments don't work
echo "hello"; doesn't work

I'd like to change the banner depending on what page is
displayed and putting the banner directly in the page
would limit it to the content section.