'receptacle' is the string variable to receive the data;
'object' is the object whose strings are to be retrieved
'index' is the index of the string to be retrieved.
For example, if the object is a data set or a data set filter, the function returns the name of the taxon at i-th position.
If the object is a dependent variable, GetString will return the formula of the dependance.
Additionally, if 'object' is one of the following literals, the following will be returned:
'LikelihoodFunction' - identifier of 'index' likelihood function (use 'rows' command to get the count of all likelihood functions).
'DataSet' - identifier of 'index' data set (use 'rows' command to get the count of all data sets).
'DataSetFilter - identifier of 'index' data set filter (use 'rows' command to get the total count)
'LAST_MODEL_PARAMETER_LIST' - identifier of 'index' parameter of the last defined model (use 'rows' command to get the total count).