A useful distinction
A prototype may omit saving, mobile controls or a complete set of levels. Clear limits let people judge the intended experiment without assuming finished-product behaviour. A polished image alone does not establish that these features exist.
Put it into practice
List the supported interactions, known omissions and tested environments in plain words. Distinguish planned features from available ones. Use the list when collecting feedback, and revise it after a verified change so the description remains connected with the actual build.