No type is associated with the object, so you can modify this structure freely.
每个对象并不与类型相关，所以可以自由地修改这种结构。
2
While some programs look up and modify the values contained in XML documents, others modify the structure of the document itself by adding and removing nodes.
一些程序查询和修改XML文档中包含的值，而其它程序则通过添加和除去节点来修改文档本身的结构。
3
You build a simple calculator application and, in subsequent iterations, improve its look and feel, modify its structure to add dependency injection, and implement JSF's navigation mechanism.