adds all the given variables to this variable container.
The method
VariableContainer.setVariables(Map) is the same as this method, but
it was added for naming consitency.
adds all the given variables to this variable container. It doesn't
remove any existing variables unless they are overwritten by the given
variables.
This method is the same as
VariableContainer.addVariables(Map) and this method
was added for naming consistency.