As detailed as possible. Please use an appendix as a way to provide full details of experimental conditions, measures, and the like. Report everything that you would in a traditional paper, including power analyses, experimental stimuli, question wording, details about measurement (e.g., recoding, factor analysis, etc.), rationales for excluding data, details about statistical models, thresholds for inferential statistics, etc.
As is the case with a traditional paper, the burden is on the author(s) to organize the information in a way that is clear and accessible to reviewers.