write intro for Syntax Highlighting; document how to create a custom adapter

- explain what source highlighting is
- explain difference between client-side and build-time syntax highlighter
- rework table that summarizes built-in syntax highlighters
- clarify that Asciidoctor does not apply syntax highlighting when producing DocBook
- add page about how to create a custom adapter

1 files changed, 25 insertions, 0 deletions

diff --git a/docs/modules/syntax-highlighting/examples/syntax-highlighter-prism.rb b/docs/modules/syntax-highlighting/examples/syntax-highlighter-prism.rb
new file mode 100644
index 00000000..8233c83e
--- /dev/null
+++ b/docs/modules/syntax-highlighting/examples/syntax-highlighter-prism.rb
@@ -0,0 +1,25 @@
+class PrismSyntaxHighlighter < Asciidoctor::SyntaxHighlighter::Base
+  register_for 'prism'
+
+  def format node, lang, opts
+    opts[:transform] = proc do |pre, code|
+      code['class'] = %(language-#{lang}) if lang
+    end
+    super
+  end
+
+  def docinfo? location
+    location == :footer
+  end
+
+  def docinfo location, doc, opts
+    base_url = doc.attr 'prismdir', %(#{opts[:cdn_base_url]}/prism/1.15.0)
+    slash = opts[:self_closing_tag_slash]
+    unless (theme_name = doc.attr 'prism-style', 'prism') == 'prism'
+      theme_name = %(prism-#{theme_name})
+    end
+    %(<link rel="stylesheet" href="#{base_url}/themes/#{theme_name}.min.css"#{slash}>
+<script src="#{base_url}/prism.min.js"></script>
+<script src="#{base_url}/components/prism-ruby.min.js"></script>)
+  end
+end