+ /** Generate a specialized XLine*.
+ * @param set_time Time this line was created
+ * @param duration Duration of the line
+ * @param source The sender of the line, nickname or server
+ * @param reason The reason for the line
+ * @param xline_specific_mask The mask string for the line, specific to the XLine type being created.
+ * @return A specialized XLine class of the given type for this factory.
+ */