In MS SQL Server, the EXPLICIT mode (of a FOR XML clause) provides the most flexibility in generating the XML you want from a query result.
The EXPLICIT mode allows more control over the shape of the XML. You can mix attributes and elements at will in deciding the shape of the XML.
It requires a specific format for the resulting rowset that is generated because of query execution. This rowset format is then mapped into XML shape.
The power of EXPLICIT mode is to mix attributes and elements at will, create wrappers and nested complex properties, create space-separated values and mixed contents.
However, writing EXPLICIT mode queries can be cumbersome.