Phing buildfiles are written in XML, and so you will need to know at least some basic things about XML to understand the following chapter. There is a lot of information available on the web:
The Standard Recommendation of XML by the W3C http://www.w3.org/TR/2000/REC-xml: very technical but exhaustive.
XML In 10 Points http://www.w3.org/XML/1999/XML-in-10-points: Quick introduction into XML.
A technical introduction to XML http://www.xml.com/pub/a/98/10/guide0.html: Interesting article by the creator of DocBook.
A valid Phing buildfile has the following basic structure: