To be added as on optional param to 

to https://documentation.magnolia-cms.com/display/DOCS62/restfn

See: https://git.magnolia-cms.com/projects/MODULES/repos/rest-client/diff/magnolia-rest-client/src/main/java/info/magnolia/rest/client/templating/RestTemplatingFunctions.java?until=d81c192641135fc2c7f925a18d61565d9bd24502

Maybe worth mentioning with body in GET that 

A payload within a GET request message has no defined semantics;
sending a payload body on a GET request might cause some existing
implementations to reject the request.
https://tools.ietf.org/html/rfc7231#section-4.3.1

See also the changes in examples affected by:
 https://git.magnolia-cms.com/projects/MODULES/repos/rest-client/pull-requests/60/diff#magnolia-rest-client/src/main/java/info/magnolia/rest/client/templating/RestTemplatingFunctions.java