Topic summary
S-expressions
Extracted from the Wikipedia article S-expression.
Relation to XML
S-expressions are often compared to XML: one key difference is that S-expressions have just one form of containment, the dotted pair, while XML tags can contain simple attributes, other tags, or CDATA, each using different syntax. Another is that S-expressions do not define a reference mechanism, whereas XML provides a notion of unique identifiers and references to them. For simple use cases, S-expressions are simpler than XML, but for more advanced use cases, XML has a query language called XPath which many tools and third party libraries use to simplify the handling of XML data.