diff --git a/labs/lib/osbash/virtualbox.functions b/labs/lib/osbash/virtualbox.functions
index 715a2ad0..f73687aa 100644
--- a/labs/lib/osbash/virtualbox.functions
+++ b/labs/lib/osbash/virtualbox.functions
@@ -5,6 +5,10 @@
 VBM=vbm
 : ${VBM_LOG:=$LOG_DIR/vbm.log}
 
+# vbm is a wrapper around the VirtualBox VBoxManage executable; it handles
+# logging and conditional execution (set OSBASH= to prevent the actual call to
+# VBoxManage, or WBATCH= to keep a call from being recorded for Windows batch
+# files)
 function vbm {
     ${WBATCH:-:} wbatch_log_vbm "$@"