<select multiple=’multiple’ name=’THEGETFIELDNAMECODE[]’ style=’width: 99%;’>
replace THEGETFIELDNAMECODE with $this->get_field_name(‘name’);
You use the get field name thing so that wordpress can format the name so that it’s engine can properly receive your data.
Just remember that web browsers don’t create arrays for you. So you need to trick your php backend with a name like somename[].