I was looking to specifying a TLS version (basically a minimum TLS version in newer versions of curl) with a max TLS version (-tls-max option in curl). tclcurl supports using 1 or the other inside of the -sslversion option. It is not possible to set both at once with this option. This option sets CURLOPT_SSLVERSION. Unfortunately, libcurl does not support setting the max TLS version in its own option, so it isn't easy to just add another tclcurl option to set this.

https://curl.se/libcurl/c/CURLOPT_SSLVERSION.html

Curl allows us to set both at the same time with a bitwise or operation. I have tested some local changes with adding an option -sslversionandmax to take a 2 element list. I am submitting a pull request.