diff --git a/runtime/doc/syntax.txt b/runtime/doc/syntax.txt
index 8a5e5f4..17f8139 100644
--- a/runtime/doc/syntax.txt
+++ b/runtime/doc/syntax.txt
@@ -214,10 +214,10 @@
 thing.  These are then linked to a highlight group that specifies the color.
 A syntax group name doesn't specify any color or attributes itself.
 
-The name for a highlight or syntax group must consist of ASCII letters, digits
-and the underscore.  As a regexp: "[a-zA-Z0-9_]*".  However, Vim does not give
-an error when using other characters.  The maximum length of a group name is
-about 200 bytes.  *E1249*
+The name for a highlight or syntax group must consist of ASCII letters,
+digits, underscores, dots, or hyphens.  As a regexp: "[a-zA-Z0-9_.-]*".
+However, Vim does not give an error when using other characters.  The maximum
+length of a group name is about 200 bytes.  *E1249*
 
 To be able to allow each user to pick their favorite set of colors, there must
 be preferred names for highlight groups that are common for many languages.