A close examination of most DTDs, however, reveals a fair degree of flexibility-particularly if the DTD is from a generic source or derived from a standard or specification.
Using standard message flow manipulation logic, the value at the tree location could be defined statically, computed from message content, or even derived from an external source.
使用标准消息流操作逻辑，该树位置处的值可以静态地定义、根据消息内容计算得出，或者从外部来源得出。
3
The numbers indicate the ratios; the colors indicate where the ratios fit into the industry-standard ranges (derived from numerous open source projects).