Sets the base URI for all XSLT transformations, the base
URI is used with Xpath instructions to resolve document() and
other commands which access external resources. It is also
used to resolve URIs for the xsl:include and
xsl:import elements.
As of 4.3, the default base URI is the directory of the
executing script. In effect, it is the directory name value
of the __FILE__ constant.
Prior to 4.3, the default base URI was less predictable.
注: Please note that file:// is needed in front of path if you use Windows.