class Kramdown::Converter::Base

def extract_code_language!(attr)

*Warning*: This version will modify the given attributes if a language is present.

See #extract_code_language 
def extract_code_language!(attr)
  lang = extract_code_language(attr)
  attr['class'] = attr['class'].sub(/\blanguage-\w+\b/, '').strip if lang
  attr.delete('class') if lang && attr['class'].empty?
  lang
end