--- a/hgext/extdiff.py	Fri Oct 12 17:57:36 2018 +0200
+++ b/hgext/extdiff.py	Sat Oct 13 02:17:41 2018 -0700
@@ -338,6 +338,7 @@
     [('p', 'program', '', _('comparison program to run'), _('CMD')),
      ] + extdiffopts,
     _('hg extdiff [OPT]... [FILE]...'),
+    helpcategory=command.CATEGORY_FILE_CONTENTS,
     inferrepo=True)
 def extdiff(ui, repo, *pats, **opts):
     '''use external program to diff repository (or selected files)