Includes the specified file name as if its contents would be written instead of the include property. The only exception is the include statement itself. When the included files contains other include statements or report definitions, the filenames are relative to file where they are defined in. include commands can be used in the project header, at global scope or between property declarations of tasks, resources, and accounts.
For technical reasons you have to supply the optional pair of curly brackets if the include is followed immediately by a macro call that is defined within the included file.