Projectional editors are a technique to manipulate the syntax tree of a structured document. While such techniques are still not main-stream in software development, they play a noteworthy role in research. While the original goal of such editors is to prevent users from syntax-errors, recent studies have shown only a relatively small effect if they are used in daily software development. However, in our understanding such editors reveal their main benefit in situations where people are not that familiar with the syntax of the document they are about to write or to change. This paper presents a randomized control trial where participants were using a projectional editor to write a structured document whose structure was not known to them upfront. The result of the study is an extremely high effect in productivity for the group using the projectional editor in comparison to the group using a pure text editor.