Without a primary file the IDE compiles/runs the source of the active window when a program is started. If a primary file is specified, the IDE always compiles/runs this source, even if another source window is active. With the menu item ”Compile—Primary file...” a file dialog can be opened where the primary file can be selected. Only the menu item ”Compile—Compile” compiles the active window regardless. This is useful if a large project is being edited, and only the syntax of the current source should be checked.
The menu item ”Compiler—Clear primary file” restores the default behavior of the IDE, i.e. the ’compile’ and ’run’ commands apply to the active window.