+{
+ glk_schannel_set_volume_ext(chan, vol, 0, 0);
+}
+
+/**
+ * glk_schannel_set_volume_ext:
+ * @chan: Channel to set the volume of.
+ * @vol: Integer representing the volume; 0x10000 is 100%.
+ * @duration: Length of volume change in milliseconds, or 0 for immediate.
+ * @notify: If nonzero, requests a notification when the volume change finishes.
+ *
+ * [DRAFT SPEC]
+ *
+ * Sets the volume in the channel, from 0 (silence) to 0x10000 (full volume).
+ * Again, you can overdrive the volume by setting a value greater than 0x10000,
+ * but this is not recommended.
+ *
+ * If the @duration is zero, the change is immediate. Otherwise, the change
+ * begins immediately, and occurs smoothly over the next @duration milliseconds.
+ *
+ * The @notify value should be nonzero in order to request a volume notification
+ * event. If you do this, when the volume change is completed, you will get an
+ * event with type #evtype_VolumeNotify. The window will be %NULL, @val1 will be
+ * zero, and @val2 will be the nonzero value you passed as @notify.
+ *
+ * The glk_schannel_set_volume() does not include @duration and @notify values.
+ * Both are assumed to be zero: immediate change, no notification.
+ *
+ * You can call these functions between sounds, or while a sound is playing.
+ * However, a zero-duration change while a sound is playing may produce
+ * unpleasant clicks.
+ *
+ * At most one volume change can be occurring on a sound channel at any time. If
+ * you call one of these functions while a previous volume change is in
+ * progress, the previous change is interrupted. The beginning point of the new
+ * volume change should be wherever the previous volume change was interrupted
+ * (rather than the previous change's beginning or ending point).
+ *
+ * Not all libraries support thse functions. You should test the appropriate
+ * gestalt selectors before you rely on them; see "Testing for Sound
+ * Capabilities".
+ */
+void
+glk_schannel_set_volume_ext(schanid_t chan, glui32 vol, glui32 duration, glui32 notify)