The potential positive effect of text highlighting on comprehension and retention has been shown by psychological studies. As program code is a special case of text, in this concept paper we propose to investigate whether code comprehension can also benefit from highlighting in a similar way. To elicit requirements for a corresponding tool, we have studied the related literature from cognitive and educational psychology including studies concerned with highlighting on paper and in digital texts as well as literature on related software development tools. We propose Highlighter, a plugin for IntelliJ IDEA that fulfills these requirements and allows highlighting arbitrary sections of code in flexible styles inspired by on-paper highlighting as well as editing and browsing the highlights inspired by digital text highlighting tools. A field test including six users indicates that our plugin fulfills the requirements, is unobtrusive and seamlessly integrates with other operations in IDEs. The initial results are promising and a larger user study is now well prepared.