Let us say we have a variable called foo. Foo has the value: index_html The difference between <dtml-var "_[foo]"> and <dtml-var "_['foo']"> is that <dtml-var "_['foo']"> will display "index_html" and <dtml-var "_[foo]"> will try render the *object* called index_html. In the former, you are asking for the contents of the foo variable. In the latter you are wanting an object that has the id that matches the contents of the foo variable.