diff --git a/runtime/doc/syntax.txt b/runtime/doc/syntax.txt
index b1176a0..418b64c 100644
--- a/runtime/doc/syntax.txt
+++ b/runtime/doc/syntax.txt
@@ -3135,8 +3135,10 @@
 conceal						*conceal* *:syn-conceal*
 
 When the "conceal" argument is given, the item is marked as concealable.
-Whether or not it is actually concealed depends on the setting on the
-'conceallevel' option.
+Whether or not it is actually concealed depends on the value of the
+'conceallevel' option.  If 'modifiable' option is on, concealable items
+in the current line are always displayed unconcealed to be able to edit
+the line.
 
 concealends						*:syn-concealends*