This information is part of the Modelica Standard Library maintained by the Modelica Association.
A simple type or component of a simple type may have the annotation
Note that this is only relevant for components of a few specific types.
false, then the variable defines a relative quantity, and if
true an absolute quantity.
annotation"(" absoluteValue "=" ( false | true ) ")
When converting between units (in the user-interface for plotting and entering parameters), the offset must be ignored, for a variable defined with annotation
absoluteValue = false.
This annotation is used in the Modelica Standard Library for example in Modelica.SIunits for the type definition TemperatureDifference.