It also details in concrete terms the composition of the three tokens (a plussign, a minus sign, and an integer) that the parser expects to encounter while scanning through the input stream.
它还详细描述了三个记号(加号、减号和整数)组合的具体项，解析器在扫描整个输入流时希望遇到这些项。
2
It has changed from a minussign to a plus sign because of this positive acceleration.
速度的符号已经，由负变正了，可是加速度又还是正的。
3
Notice the difference: there's a plussign here;there's a minus sign here.