Update runtime files.
diff --git a/runtime/syntax/help.vim b/runtime/syntax/help.vim
index 693a113..673a54f 100644
--- a/runtime/syntax/help.vim
+++ b/runtime/syntax/help.vim
@@ -1,7 +1,7 @@
" Vim syntax file
" Language: Vim help file
" Maintainer: Bram Moolenaar (Bram@vim.org)
-" Last Change: 2017 Oct 19
+" Last Change: 2019 May 12
" Quit when a (custom) syntax file was already loaded
if exists("b:current_syntax")
@@ -11,7 +11,7 @@
let s:cpo_save = &cpo
set cpo&vim
-syn match helpHeadline "^[-A-Z .][-A-Z0-9 .()]*[ \t]\+\*"me=e-1
+syn match helpHeadline "^[-A-Z .][-A-Z0-9 .()_]*[ \t]\+\*"me=e-1
syn match helpSectionDelim "^===.*===$"
syn match helpSectionDelim "^---.*--$"
if has("conceal")