XML (Extensible Markup Language) is a markup-based format for structured information. In web APIs, it can carry messages exchanged between systems. SOAP uses XML for its requests and responses; HTTP commonly transports those messages, though SOAP can use other protocols. section 1.1.4
XML also appears in WSDL files, which describe the operations and messages supported by SOAP endpoints. SOAP can be extended with additional message-level standards, but its XML requests and responses can become extremely complex. When evaluating an API approach, distinguish the message format (XML) from the messaging protocol (SOAP) and its transport (often HTTP). section 1.1.4




