# File lib/math_ml/latex.rb, line 320
                        def expand_environment(env, body, params, opt=nil)
                                return nil unless @environments.has_key?(env)
                                e = @environments[env]
                                opt = e.option if e.option && !opt
                                params.unshift(opt) if e.option
                                raise ParseError.new("Need more parameter.") if params.size < e.num

                                bg = e.beginning.gsub(/(#{MBEC}*?)\#(\d+)/) do
                                        $1.to_s << params[$2.to_i-1]
                                end

                                en = e.ending.gsub(/(#{MBEC}*?)\#(\d+)/) do
                                        $1.to_s << params[$2.to_i-1]
                                end

                                " #{bg} #{body} #{en} "
                        end