# File lib/math_ml/latex.rb, line 87
                        def scan_block
                                return nil unless scan(/\{/)
                                block = "{"
                                bpos = pos-1
                                nest = 1
                                while _scan(/(#{MBEC}*?)([\{\}])/)
                                        block << matched
                                        case self[2]
                                        when "{"
                                                nest+=1
                                        when "}"
                                                nest-=1
                                                break if nest==0
                                        end
                                end
                                if nest>0
                                        self.pos = bpos
                                        raise BlockNotClosed
                                end
                                self.pos = bpos
                                _scan(/\A\{(#{Regexp.escape(block[RE::BLOCK, 1].to_s)})\}/)
                        end