Name of the attribute to query. Either 'sf_column' or
'agr'.
active
Which network element (i.e. nodes or edges) to activate before
extracting. If NULL, it will be set to the current active element of
the given network. Defaults to NULL.
Value
The value of the attribute matched, or NULL if no exact
match is found.
Details
sf attributes include sf_column (the name of the sf column)
and agr (the attribute-geometry-relationships).