From 27f6f31e16cc676b30edb0bc3ef2b0a2faec9b39 Mon Sep 17 00:00:00 2001
From: Teddy Wing
Date: Thu, 27 Oct 2022 22:02:09 +0200
Subject: Add documentation for SSVLAudioServicesPropertySystemAlertVolume

---
 SSVLSystemAlertVolume.c | 7 +++++++
 1 file changed, 7 insertions(+)

(limited to 'SSVLSystemAlertVolume.c')

diff --git a/SSVLSystemAlertVolume.c b/SSVLSystemAlertVolume.c
index 4f6c270..8e50195 100644
--- a/SSVLSystemAlertVolume.c
+++ b/SSVLSystemAlertVolume.c
@@ -10,6 +10,13 @@
 
 #include "SSVLSystemAlertVolume.h"
 
+// This property appears to be private, as it isn't defined in Apple's MacOSX
+// SDK framework headers.
+//
+// The value comes from the Sound preference pane. Disassembling the
+// `/System/Library/PreferencePanes/Sound.prefPane/Contents/MacOS/Sound` binary
+// shows that functions accessing the system alert volume do so via the
+// '0x7373766c' property. Converting that to a FourCharCode yields 'ssvl'.
 const AudioServicesPropertyID SSVLAudioServicesPropertySystemAlertVolume = 'ssvl';
 
 OSStatus SSVLGetSystemVolume(Float32 *volume) {
-- 
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