Well-Formed XML
For an XML document to be considered valid, it must satisfy the following restrictions:
The document must have only one top-level element. This element is called the root element.
Every element must have both a start and an end tag.
All attributes must have values, and those values must be quoted.
Elements must not overlap. You cannot use
<a><b></a></b>, because the ending</a>tag comes before</b>.You must convert &, <, and > to their entity equivalents. You can use
htmlentities( )to solve this.
When a document meets these rules, itâs valid, or well-formed, XML.
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