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: 注意如果使用 Windows，需要在路径前加上 file://。