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While system variables come with predefined comments, it's up to your to document your own variables using the Comment field. Good comments explain what a variable is used for, where its value comes from, and what a typical value looks like.
Project Information
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Remarks
The project itself has notes that can be edited on the Project Information page. This field is by default shown on the Welcome Page. You can put a brief summary of the purpose of the project, and possibly some history or other notes.
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