Thanks so much for your reply. I was confused by the fact that there was no code to be executed within the if statement.
if (true) {
no code here
}
from your explanation, I see that the function dynamic_sidebar() is executed while the if statement is evaluated, if the function exists. If I understand your response correctly, the following snippet would have the same result:
<?php if (function_exists('dynamic_sidebar')) {dynamic_sidebar();} ?>