# File lib/math_ml/latex.rb, line 737
                        def cmd_entity
                                param = @scanner.scan_block ? @scanner[1] : @scanner.scan(/./)
                                raise ParseError.new("Need parameter.") unless param
                                unless @unsecure_entity || @entities[param]
                                        param =@scanner.matched[/\A\{#{RE::SPACE}*(.*\})\z/, 1] if @scanner.matched=~RE::BLOCK
                                        @scanner.pos = @scanner.pos-(param.size)
                                        raise ParseError.new("Unregistered entity.")
                                end
                                Operator.new << entitize(param)
                        end