# File lib/math_ml/latex.rb, line 304
                        def expand_command(com, params, opt=nil)
                                return nil unless @commands.has_key?(com)
                                c = @commands[com]
                                opt = c.option if c.option && !opt
                                params.unshift(opt) if c.option
                                raise ParseError.new("Need more parameter.") if params.size < c.num

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