diff --git a/benchmark/regexp-vs-include.rb b/benchmark/regexp-vs-include.rb
new file mode 100644
index 00000000..b2a4eff4
--- /dev/null
+++ b/benchmark/regexp-vs-include.rb
@@ -0,0 +1,51 @@
+#!/usr/bin/env ruby
+require 'benchmark/ips'
+
+# For this pull request, which changes Page#dir
+# https://github.com/jekyll/jekyll/pull/4403
+
+CONTENT_CONTAINING = <<-HTML.freeze
+<!DOCTYPE HTML>
+<html lang="en-US">
+  <head>
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
+    <meta charset="UTF-8">
+    <title>Jemoji</title>
+    <meta name="viewport" content="width=device-width,initial-scale=1">
+    <link rel="stylesheet" href="/css/screen.css">
+  </head>
+  <body class="wrap">
+    <p><img class="emoji" title=":+1:" alt=":+1:" src="https://assets.github.com/images/icons/emoji/unicode/1f44d.png" height="20" width="20" align="absmiddle"></p>
+
+  </body>
+</html>
+HTML
+CONTENT_NOT_CONTAINING = <<-HTML.freeze
+<!DOCTYPE HTML>
+<html lang="en-US">
+  <head>
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
+    <meta charset="UTF-8">
+    <title>Jemoji</title>
+    <meta name="viewport" content="width=device-width,initial-scale=1">
+    <link rel="stylesheet" href="/css/screen.css">
+  </head>
+  <body class="wrap">
+    <p><img class="emoji" title=":+1:" alt=":+1:" src="https://assets.github.com/images/icons/emoji/unicode/1f44d.png" height="20" width="20" align="absmiddle"></p>
+
+  </body>
+</html>
+HTML
+
+Benchmark.ips do |x|
+  x.report("no body include?") { CONTENT_NOT_CONTAINING.include?('<body') }
+  x.report("no body regexp")   { CONTENT_NOT_CONTAINING =~ /<\s*body/ }
+  x.compare!
+end
+
+# No trailing slash
+Benchmark.ips do |x|
+  x.report("with body include?") { CONTENT_CONTAINING.include?('<body') }
+  x.report("with body regexp")   { CONTENT_CONTAINING =~ /<\s*body/ }
+  x.compare!
+end
