XML文档如下：
<?xml version="1.0" encoding="utf-8"?>
<Design id="1" name="数学表达式设计(A+B=C)">
<Nodes>
<Node Id="1" Text="开始" Type="BEGIN" Index="1" />
<Node Id="2" Text="C" Type="NUM" Index="2" />
<Node Id="3" Text="=" Type="EQUAL" Index="3" />
<Node Id="4" Text="+" Type="ADD" Index="4" />
<Node Id="5" Text="A" Type="NUM" Index="5" />
<Node Id="6" Text="B" Type="NUM" Index="6" />
</Nodes>
<Lines>
<Line ID="101" Text="" Type="LINE" Srcnode="1" Tarnode="2" Index="84" />
<Line ID="102" Text="" Type="LINE" Srcnode="2" Tarnode="3" Index="85" />
<Line ID="103" Text="" Type="LINE" Srcnode="3" Tarnode="4" Index="86" />
<Line ID="104" Text="" Type="LINE" Srcnode="4" Tarnode="5" Index="87" />
<Line ID="105" Text="" Type="LINE" Srcnode="5" Tarnode="4" Index="88" />
<Line ID="106" Text="" Type="LINE" Srcnode="6" Tarnode="4" Index="89" />
</Lines>
</Design>
