Params is a read-only TStrings property used to store the parsed values for HTTP headers in the HTTP request. 

Params contains the header values after TIdURI.URLDecode has been used to convert the headers to their ASCII representation. 

In accordance with RFC 1866 section 8.2.1., all "+" characters (Decimal 43) in UnparsedParams are converted to a Space character (Decimal 32) prior to being decoded and added to the values in the property. 

Use UnparsedParams to view the HTTP headers in their URL-encoded form. 

Params is updated by TIdHTTPServer when a peer thread generates a new HTTP request.

TIdHTTPServer 

UnparsedParams