Gemfile: add html-proofer and mdl.

Gemfile

@@ -11,3 +11,8 @@ gem "jekyll-remote-theme"
 gem "jekyll-seo-tag"
 gem "jekyll-sitemap"
 gem "rake"
+
+group :test do
+  gem "html-proofer"
+  gem "mdl"
+end

Gemfile.lock

@@ -1,14 +1,28 @@
 GEM
   remote: https://rubygems.org/
   specs:
+    Ascii85 (1.1.1)
     addressable (2.8.6)
       public_suffix (>= 2.0.2, < 6.0)
+    afm (0.2.2)
+    async (2.12.0)
+      console (~> 1.25, >= 1.25.2)
+      fiber-annotation
+      io-event (~> 1.6)
     bigdecimal (3.1.8)
+    chef-utils (18.4.12)
+      concurrent-ruby
     colorator (1.1.0)
     concurrent-ruby (1.3.3)
+    console (1.25.2)
+      fiber-annotation
+      fiber-local (~> 1.1)
+      json
     em-websocket (0.5.3)
       eventmachine (>= 0.12.9)
       http_parser.rb (~> 0)
+    ethon (0.16.0)
+      ffi (>= 1.15.0)
     eventmachine (1.2.7)
     faraday (2.9.1)
       faraday-net_http (>= 2.0, < 3.2)
@@ -21,6 +35,10 @@ GEM
     ffi (1.17.0-arm64-darwin)
     ffi (1.17.0-x86_64-darwin)
     ffi (1.17.0-x86_64-linux-gnu)
+    fiber-annotation (0.2.0)
+    fiber-local (1.1.0)
+      fiber-storage
+    fiber-storage (0.1.1)
     forwardable-extended (2.6.0)
     google-protobuf (4.27.1)
       bigdecimal
@@ -37,9 +55,20 @@ GEM
     google-protobuf (4.27.1-x86_64-linux)
       bigdecimal
       rake (>= 13)
+    hashery (2.1.2)
+    html-proofer (5.0.9)
+      addressable (~> 2.3)
+      async (~> 2.1)
+      nokogiri (~> 1.13)
+      pdf-reader (~> 2.11)
+      rainbow (~> 3.0)
+      typhoeus (~> 1.3)
+      yell (~> 2.0)
+      zeitwerk (~> 2.5)
     http_parser.rb (0.8.0)
     i18n (1.14.5)
       concurrent-ruby (~> 1.0)
+    io-event (1.6.4)
     jekyll (4.3.3)
       addressable (~> 2.4)
       colorator (~> 1.0)
@@ -71,6 +100,7 @@ GEM
       jekyll (>= 3.7, < 5.0)
     jekyll-watch (2.2.1)
       listen (~> 3.0)
+    json (2.7.2)
     kramdown (2.4.0)
       rexml
     kramdown-parser-gfm (1.1.0)
@@ -79,19 +109,49 @@ GEM
     listen (3.9.0)
       rb-fsevent (~> 0.10, >= 0.10.3)
       rb-inotify (~> 0.9, >= 0.9.10)
+    mdl (0.13.0)
+      kramdown (~> 2.3)
+      kramdown-parser-gfm (~> 1.1)
+      mixlib-cli (~> 2.1, >= 2.1.1)
+      mixlib-config (>= 2.2.1, < 4)
+      mixlib-shellout
     mercenary (0.4.0)
+    mixlib-cli (2.1.8)
+    mixlib-config (3.0.27)
+      tomlrb
+    mixlib-shellout (3.2.8)
+      chef-utils
     net-http (0.4.1)
       uri
+    nokogiri (1.16.6-aarch64-linux)
+      racc (~> 1.4)
+    nokogiri (1.16.6-arm-linux)
+      racc (~> 1.4)
+    nokogiri (1.16.6-arm64-darwin)
+      racc (~> 1.4)
+    nokogiri (1.16.6-x86_64-darwin)
+      racc (~> 1.4)
+    nokogiri (1.16.6-x86_64-linux)
+      racc (~> 1.4)
     pathutil (0.16.2)
       forwardable-extended (~> 2.6)
+    pdf-reader (2.12.0)
+      Ascii85 (~> 1.0)
+      afm (~> 0.2.1)
+      hashery (~> 2.0)
+      ruby-rc4
+      ttfunk
     public_suffix (5.0.5)
+    racc (1.8.0)
+    rainbow (3.1.1)
     rake (13.2.1)
     rb-fsevent (0.11.2)
     rb-inotify (0.11.1)
       ffi (~> 1.0)
     rexml (3.3.0)
       strscan
     rouge (4.2.1)
+    ruby-rc4 (0.1.5)
     rubyzip (2.3.2)
     safe_yaml (1.0.5)
     sass-embedded (1.77.5-aarch64-linux-gnu)
@@ -107,9 +167,16 @@ GEM
     strscan (3.1.0)
     terminal-table (3.0.2)
       unicode-display_width (>= 1.1.1, < 3)
+    tomlrb (2.0.3)
+    ttfunk (1.8.0)
+      bigdecimal (~> 3.1)
+    typhoeus (1.4.1)
+      ethon (>= 0.9.0)
     unicode-display_width (2.5.0)
     uri (0.13.0)
     webrick (1.8.1)
+    yell (2.2.2)
+    zeitwerk (2.6.15)
 
 PLATFORMS
   aarch64-linux
@@ -120,11 +187,13 @@ PLATFORMS
 
 DEPENDENCIES
   faraday-retry
+  html-proofer
   jekyll
   jekyll-redirect-from
   jekyll-remote-theme
   jekyll-seo-tag
   jekyll-sitemap
+  mdl
   rake
 
 RUBY VERSION