What do graphical user interface (GUI) HTML editor applications allow users to do?

Graphical user interface (GUI) HTML editor applications are designed primarily to simplify the process of creating and editing HTML content. These tools provide a visual representation of web pages, allowing users to manipulate and format content in a way that doesn't necessitate a deep understanding of the underlying HTML code.

The correct answer is focused on manual code modification, indicating that while these applications may assist users with visual editing features, they also allow users to directly interact with and modify the HTML code itself if they choose. This dual capability supports both novice and experienced developers, as it offers a balance between visual design and code level access.

Other options reflect functionalities that are either not primary to the role of GUI HTML editors or pertain to different areas of web development. For example, the automation of server management is unrelated to the functionality of HTML editors, which focus on client-side design rather than server operations. Similarly, although CSS modification can be part of the editing process, it does not encompass the primary role of HTML editors, which is more clearly about HTML. Lastly, designing graphics typically involves graphic design software rather than HTML editors, which focus on markup and layout rather than graphic creation.