This is more a rant than a question.
In the old Map Viewer (now called 'classic'), when running analysis your output dataset names could include hyphen and bracket/brace characters. In the new Map Viewer, if you include a hyphen or bracket/brace character in the name of the output dataset you get the following message:
However, if you visit the page linked in this message (https://doc.arcgis.com/en/arcgis-online/analyze/perform-analysis-mv.htm#ESRI_SECTION1_5EACA346CAB14E...), the hyphen and bracket/brace characters are not included in the list of disallowed characters:
Aaaaaaaaaaaaaaaaaaaaaaargh.
This is either a documentation error or a bug in the Analysis tools in the new Map Viewer. Either way, it's really annoying.