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+Top-level
+=========
+
+A ZScript file can have one of several things at the top level of the file:
+
+- Class definitions
+- Structure definitions
+- Enumeration definitions
+- Constant definitions
+- Include directives
+
+Class definitions
+=================
+
+A class definition starts with a class header, followed by an opening brace, class data and a closing brace. Alternatively, you can follow the class header with a semicolon and the rest of the file will be considered class data.
+
+Class headers
+-------------
+
+The class header is formed as such:
+
+```cs
+   class Name [: BaseClass] [Class flags...]
+```
+
+Class flags include:
+
+| Flag                  | Description |
+| --------------------- | --- |
+| abstract              | Cannot be instantiated with new(). |
+| native                | Class is from the engine. |
+| ui                    | Has UI scope. |
+| play                  | Has Play scope. |
+| replaces ReplaceClass | Replaces ReplaceClass with this class. Only works on objects which are descendants of Actor. |
+| version("ver")        | Restricted to version <ver>. |
+
+Example usages:
+
+```cs
+   class MyCoolObject play // automatically inherits Object
+   class MyCoolThinker : Thinker // inherits Thinker
+   class MyCoolActor : Actor replaces OtherActor
+   class MyCoolInterface abstract // can only be inherited
+```