If I run term_start('zsh', {'term_name': 'MYTER','vertical': v:true})
I get the expected behavior, but if I run term_start('zsh', {'term_name': 'MYTER','belowright': v:true})
will produce E475: Invalid argument: belowright
, in-spite from the doc one can read
"vertical" split the window vertically; note that other window position can be defined with command modifiers, such as :belowright.
I am using MacVim 9.0.