解析器有不同的阶段，解析一行时。结果
因此，前百分之pressions都在一条线或块被解析，则执行线路（或在块中的任何行）之前展开。

因此​​，在执行时，他们无法更改。

 组VAR =由来
回声＃1％VAR％
（
  组VAR =新价值
  回音2％VAR％
）
回声＃3％VAR％
 

它输出

 ＃1由来
＃2原点
＃3新的价值
 

由于在分析时＃2将扩大到原产地块的任意行之前执行。
所以，你可以在＃3块之后看到新的数值。

在此相反，推迟扩张扩大了执行行之前的每一行。

  SETLOCAL EnableDelayedExpansion
组VAR =由来
回声＃1％VAR％！VAR！
（
  组VAR =新价值
  回音2％VAR％！VAR！
）
回声＃3％VAR％！VAR！
 

输出

 ＃1起源，起源
＃2原点，新的价值
＃3新的价值，新价值
 

现在在＃2你看到同一个变量两个不同的扩展，因为当块被解析％VAR％扩大，但！无功！终止后展开行组VAR =新值被执行了。

有关批处理解析器在SO:如何在Windows命令国米preTER（CMD.EXE）解析脚本？

I am trying to learn MS Batch, and I was specifically trying to understand the "setlocal" and the "enabledelayedexpression" aspects, when I came across vocabulary I did not understand:

execution time and parse time

The parser has different phases, when parsing a single line.
So the percent expressions are all expand when a line or block is parsed, before the line (or any line in a block) is executed.

So at execution time they can't change anymore.

set var=origin
echo #1 %var%
(
  set var=new value
  echo #2 %var%
)
echo #3 %var%

It outputs

#1 origin
#2 origin
#3 new value

As at parse time #2 will be expanded to origin before any line of the block is executed. So you can see the new value just after the block at #3.

In contrast, delayed expansion is expanded for each line just before the line is executed.

setlocal EnableDelayedExpansion
set var=origin
echo #1 %var%, !var!
(
  set var=new value
  echo #2 %var%, !var!
)
echo #3 %var%, !var!

Output

#1 origin, origin
#2 origin, new value
#3 new value, new value

Now at #2 you see two different expansions for the same variable, as %var% is expanded when the block is parsed, but !var! is expanded after the line set var=new value was executed.

More details about the batch parser at SO: How does the Windows Command Interpreter (CMD.EXE) parse scripts?