upcase.rb

# An example Jekyll converter. Utilizes the new plugin system.
#
#
# 1. Make a _plugins directory in your jekyll site, and put this class in a file there.
# 2. Any file in the _posts directory ending in .upcase will be processed using this converter.

module Jekyll
  class UpcaseConverter < Converter
    safe true

    priority :low

    def matches(ext)
      ext =~ /upcase/i
    end 

    def output_ext(ext)
      ".html"
    end

    def convert(content)
      content.upcase
    end
  end
end

Will it run before of after Markdown/Kramdown parsing?