R/exams: Open-ended questions with exams2moodle

My goal is to create a question using R/exams and Moodle including a few plots generated in the Rmd exercise file. The students should describe the plots verbally and then the exercise is graded manually. Is it possible to use `exams2moodle` to create such an open-ended free text question for Moodle? There is no extype for it. In the documentation the only hint is: _"In order to generate free text questions in moodle one may specify extra parameters via `\exextra`. Currently the following options are supported:"_. I have tried to add `\exextra` parameters to the metainformation, but it did not change anything.