function Trace(
    AURL: string
): string; overload;

String - Test or diagnostic messages for the resource.

Trace is an overloaded method in TIdHTTP that implements the HTTP TRACE command verb. Trace is used to a remote application-layer loop- back for the Request message, and allows the HTTP client to see the data received at the host or proxy server that is the target for the Request. Trace will return information that can be used for testing and diagnostic purposes. 

If the Request is valid, the Response to a Trace Request will contain the entire Request message with a Content-Type of "message/http". 

Trace is overloade to allow the response content to be returned a String, using the function-based variant of the method, or in the stream specified in AResponseContent.