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diff --git a/doc/asciidoctor-macros/commaize-block/extension.rb b/doc/asciidoctor-macros/commaize-block/extension.rb
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+++ b/doc/asciidoctor-macros/commaize-block/extension.rb
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+# SPDX-License-Identifier: MIT
+require 'asciidoctor/extensions' unless RUBY_ENGINE == 'opal'
+
+include Asciidoctor
+
+# An extension that converts a list of lines to an inline Oxford comma-separated list.
+#
+# Usage
+#
+#   [commaize]
+#   --
+#   item1
+#   item2
+#   item3
+#   --
+#
+class CommaizeBlock < Extensions::BlockProcessor
+  include WsUtils
+  use_dsl
+
+  named :commaize
+  on_contexts :paragraph, :open
+  # XXX What's the difference between text, raw, simple, verbatim, etc?
+  parse_content_as :simple
+
+  def process(parent, reader, attrs)
+    lines = reader.lines
+    sort = attrs.fetch('sort', 'true') == 'true'
+
+    lines = lines.reject(&:empty?)
+    lines = lines.map(&:strip)
+    lines = lines.sort_by(&:downcase) if sort
+
+    if lines.length < 2
+      create_paragraph parent, lines, attrs
+    elsif lines.length == 2
+      create_paragraph parent, lines.join(" and "), attrs
+    else
+      commaized = lines[0..-2].join(", ")
+      commaized << ", and " + lines[-1]
+      create_paragraph parent, commaized, attrs
+    end
+  end
+end