Pattern - XML Configuration File

XML is now a common format for configuration files. It can provide a standard syntax for containing configuration data.

Features

One basic syntax to learn.
XSL engines can be used to generate XML, HTML and text content from XML source files.
Schema languages can be used to validate XML at build time, or before deployment.
XML-aware editors can make editing the files easier, especially if driven by the schema language.
Trees are easy for code to navigate.
XML namespaces allow XML from different schemas to be mixed.

Whitespace handling can be inconsistent from application to application.
XML Parsers are invariably utterly unforgiving over errors.
XML Schema has proven inordinately brittle to change. It is often the case that an XML configuration file, such as a web.xml file that validated against one version of a schema, fails to be considered valid by a later version.
No way to represent characters with an ASCII value <32 other than tab, newline and carriage return.
Base-64 encoding of binary data is very inefficient in UTF-16 encoded documents.
Every custom XML configuration syntax is a whole new XML language to learn.
Error messages, especially with XML Schema, are hard for beginners to understand.
Double minus signs - are not allowed in comments. This is source of recurrent bug reports in Ant.
Nobody really understands XML namespaces. Those that think they do still do not know whether or not the namespace ##local is implicitly part of the ##other namespace.
The tree structure is unable to represent more complex graphs without some form of cross referencing mechanism, mechanisms which are inherently non-standard.
If XPath is used to do cross referencing, then it can only refer to content within the hierarchy, even if the hierarchy is turned into a graph during deployment.
The strictly hierarchical format makes it hard to concatenate documents together.

Clearly, SmartFrog is not itself an XML format. The sf-xml package can be used to work with XML content.