A network infrastructure element such as a router or switch performs transparent and optimized validation of XML schemas of XML payloads received in the network element. The network element comprises logic for receiving and storing one or more validation scope rules that define a portion of an extensible markup language (XML) schema for validation; receiving and storing the XML schema; receiving over the network an application-layer message comprising one or more of the packets; identifying a particular XML element in an XML payload of the application-layer message, wherein the particular XML element is within the portion of the XML schema defined in the one or more validation scope rules; determining whether the particular XML element conforms to the XML schema; and performing a responsive action based on whether the particular XML element conforms to the XML schema.