Hello all, need to use the If-Modified-Since header in one of my APIs. The format requested is the IETF date format: If-Modified-Since: Wed, 21 Oct 2015 07:28:00 GMT as explained in [1]. If I pass the header as prescribed to a restxq made like: declare %rest:path("config") %rest:header-param("If-Modified-Since", "{$modifiedsince-ietf}") %rest:HEAD function config:check($modifiedsince-ietf as xs:string?){ I get the following exception: Cannot convert xs:string+ to xs:string?: ("Wed", "21 Oct 2015 07:28:00 GMT"). Which somehow demonstrates that , is treated as a separator of values for the header. I patched by replacing ? with * and using a string-join on the $modifiedsince-ietf before passing it to the follwoing parse-ietf-date function. But this is hard to explain and probably subject to other issues in the future. Is there a way to pass HTTP headers verbatim to the RestXQ function? thanks! M. [1] https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/If-Modified-Since