最近在研究svg,对其中的doc转换成GraphicsNode的具体流程不明白，求详解

[shanghai19430928]

UserAgentAdapter userAgent=new UserAgentAdapter();
ctx=new BridgeContext(
userAgent, null, new DocumentLoader(userAgent));
builder=new DynamicGVTBuilder();
ctx.setDynamicState(BridgeContext.DYNAMIC);
GraphicsNode gvt=builder.build(ctx, document);

求对此段代码的详解