用于解析 DTD 位置的目录条目

Created: November-22, 2018

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<public 
   publicId="-//OASIS//DTD DocBook XML V4.5//EN"  4
   uri="docbook45/docbookx.dtd"/>

<system
   systemId="http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"  5
   uri="docbook45/docbookx.dtd"/>

<system
   systemId="docbook4.5.dtd"    6
   uri="docbook45/docbookx.dtd"/>