Predefined symbols are used by formulas to read values from the environment (Ultra Fractal) and optionally return values to the environment. Predefined symbols are always prefixed by a # character, to avoid conflicts between variables and predefined symbols.
Most read-only predefined symbols are treated as constants, so they can be used in array declarations and in settings that accept expressions, such as default.
Not all predefined symbols can always be accessed. This depends on the formula type and the section within the formula type.
Use the Contents tab to see what predefined symbols are available.