Final answer:
Unacceptable comments on performance reports are those that lack specificity and actionability, including vague praises or unsubstantiated criticism, and fail to offer clear guidance to the writer on how to improve.
Step-by-step explanation:
Comments that are not allowed in the comments block on all performance reports typically lack specific and action-oriented feedback. Vague comments fail to deliver constructive criticism or guidance and consist of statements like "Revise this sentence," which does not clarify the reason behind the suggestion nor offers a method for improvement. Somewhat helpful comments do mention specific aspects of writing but lack detailed advice, for example, "Revise this question so that it's more debatable" merely hints at the issue without a detailed explanation or clear direction on how to address it. In contrast, specific and clear comments provide targeted feedback that helps the writer understand both the strengths and weaknesses of their work, as well as action points for improvement, such as suggesting alternative questions that lead to more substantive discussions and arguments in an essay.