patch 7.4.792
Problem:    Can only conceal text by defining syntax items.
Solution:   Use matchadd() to define concealing. (Christian Brabandt)
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index 971a202..00485e3 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -12079,7 +12079,7 @@
 
 	    c = *end;
 	    *end = NUL;
-	    match_add(curwin, g, p + 1, 10, id, NULL);
+	    match_add(curwin, g, p + 1, 10, id, NULL, NULL);
 	    vim_free(g);
 	    *end = c;
 	}