The XML family of languages is an important technology for the web, at all levels. It structures both web pages, SOAP or WSDL service-oriented application technologies, but also numerous databases accessible online, e-Book technologies, social web services, etc. In this chapter, we will rework our REST-based wiki to make it understand and produce SOAP requests. Along the way, we will introduce Opa’s advanced tools for extracting data from XML or building XML documents.