Need help customizing Regexp for Oniguruma?

Question

ruby

There is Octopress. Its files use regexp with look behind. There is Ruby, version 1.8, which by itself does not support look behind. There is Oniguruma, which, in theory, supports everything you need. I don't understand how to convert an expression of one type to a "understandable" Oniguruma. Can anyone take a look? :) Thanks.
Code example:

/<div class="entry-content">(?<content>[\s\S]*?)<\/div>\s*<(footer|\/article)>/ =~ input

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