在mvn.cmd脚本中使用valMHome有什么用处

Question

我正在浏览mvn.cmd脚本（在maven / bin中）注意到valMHome未定义。

在旧的mvn.cmd (maven 3.3.3)就像是，

:chkMHome
if not "%M2_HOME%"=="" goto valMHome

SET "M2_HOME=%~dp0.."
if not "%M2_HOME%"=="" goto valMHome

echo.
echo Error: M2_HOME not found in your environment. >&2
echo Please set the M2_HOME variable in your environment to match the >&2
echo location of the Maven installation. >&2
echo.
goto error

:valMHome

:stripMHome
if not "_%M2_HOME:~-1%"=="_\" goto checkMCmd
set "M2_HOME=%M2_HOME:~0,-1%"
goto stripMHome

在最新的mvn.cmd文件(maven 3.5.2)中就像是，

:chkMHome
set "MAVEN_HOME=%~dp0.."
if not "%MAVEN_HOME%"=="" goto valMHome
goto error

:valMHome

:stripMHome
if not "_%MAVEN_HOME:~-1%"=="_\" goto checkMCmd
set "MAVEN_HOME=%MAVEN_HOME:~0,-1%"
goto stripMHome

知道这些脚本中valMHome的作用和用途是什么？