If descriptions are assigned to the "description"
attributes of the data frame
columns, the descriptions
function will extract those values. The
function will return the description values in a named list,
where the names
correspond to the name of the column that the description was assigned to.
If a column does not have a description attribute assigned, that column
will not be included in the list.
When used on the receiving side of an assignment, the function will assign
descriptions to a data frame. The description values
should be in a named list, where
each name corresponds to the name of the data frame column to assign
values to.