GcrColumn

typedef struct {
	const gchar *property_name;     /* The property to retrieve */
	GType property_type;            /* The property type */
	GType column_type;              /* The resulting property type for this column */

	const gchar *label;             /* The label for this column, or NULL */
	GcrColumnFlags flags;           /* Column flags */

	GValueTransform transformer;    /* The way to transform to this type or NULL */

	gpointer user_data;
} GcrColumn;

enum GcrColumnFlags