# Introduction to XML#

1. The content of an XML file is composed of elements. Each element is marked by a pair of tags <tag>...</tag>.

2. The hierarchical structure of elements is important. At the same level of hierarchy, the arrangement order of elements is not important.

3. The tag names are keywords, which should not be changed.

4. Each element can have multiple attributes, which are name="value" pairs. The names are also keywords. The values must be surrounded by double quotes.