The central part of the ACGUI window is the schema Editor. From here, schema files can be viewed and edited.

To begin editing an ASN.1 schema, create or open a schema file. A new schema file can be opened by clicking New in the toolbar or by navigating to File > New Schema File. An existing schema file can be accessed via the Open button in the toolbar or navigating to File > Open File. The file is added to the current project and shown in the Editor.

The Editor window is also used to display a schema browser for navigating within a validated schema. To display the browser after validating a schema, click on an item in the ASN.1 Tree window. The browser displays a hyperlinked version of the schema, centered on the definition of the selected item. Click the names of other defined types in the browser to show their definitions.

By default, schema documents are displayed as tabs in the Editor. The Text and Browser tabs at the bottom of the window are for schema editing and hyperlinked schema browsing, respectively. Schema files currently open for edit are displayed as tabs at the top of the Text tab.