@hampy (and others): What documentation do you want us to update? Where did you look for this information? Can you post a link to the page, where you expected this information? It's documented on many places.
open sftp://xxxxxxx:email@example.com:xxxx -rawsettings ResumeSupport=1 ResumeThreshold=10240000 -hostkey="xxxxx"
open sftp://xxxxxxx:firstname.lastname@example.org:xxxx -rawsettings ResumeSupport=2 -hostkey="xxxxx"