diff --git a/src/structs.h b/src/structs.h
index 39c5ef2..5b1a5cc 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -800,7 +800,8 @@
 typedef struct textprop_S
 {
     colnr_T	tp_col;		// start column (one based, in bytes)
-    colnr_T	tp_len;		// length in bytes
+    colnr_T	tp_len;		// length in bytes, when tp_id is negative used
+				// for left padding plus one
     int		tp_id;		// identifier
     int		tp_type;	// property type
     int		tp_flags;	// TP_FLAG_ values