re = /<drawing>(?:(?!<\/drawing>).)*?<Chart>.*?<\/drawing>/
str = '<drawing><some other tags><Picture><some other tags></drawing><drawing><some other tags><Chart><some other tags></drawing>'
# Print the match result
str.scan(re) do |match|
puts match.to_s
end
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Ruby, please visit: http://ruby-doc.org/core-2.2.0/Regexp.html