Why is there an additional pair of curly braces on the Inno Setup Preprocessor:#emit page?

问题

I've been looking through Inno Setup documentation and found this:

(https://jrsoftware.org/ispphelp/index.php?topic=expressions)

Filename: "file2.ext"; DestDir: {{#MyDestDir}}

Why do we need to use an additional pair of curly braces here? Mustn't we type it like this instead DestDir: "{#MyDestDir}"?

来源：https://stackoverflow.com/questions/63036551/why-is-there-an-additional-pair-of-curly-braces-on-the-inno-setup-preprocessor