The Acme Source editor shows the Acme description of the system being edited. Changes in this editor are parsed and may affect the diagram or family editor associated with the file. Errors appear as decorations in the margin of the editor. Hovering over the decoration will display the error. If a file is opened that contains parse errors, then only the Acme Source editor is opened.
It is also possible to hide detail of the Acme description using folding. To fold or unfold a region, select a blue triangle in the left margin. AcmeStudio takes advantage of this feature to allow you to elide the detail of components, ports, connectors, roles, and representations. Representations are elided by default.