If you're thinking of whole preset Weighting Expressions, then no that's not the case. Maybe they were trying to talk about the "variables" that are pre-defined for use in the Weighting Expression, such as "EccentricitySigma" or "FHWMMax", which would be replaced with the values of the Eccentricity in Sigma units of the whole set or the maximum FHWM value of the whole set, for example. Hover over the expression text boxes for a tooltip that describes them.
Once you come up with one you like, if you save the instance as an icon on your workspace it will be there for you next time you open it.