YAML Document Audit

Report what a YAML reader will do with the text supplied, as distinct from whether the data is correct. Reports a duplicate key, which most readers accept while silently keeping the last; an unquoted YAML 1.1 boolean word such as on, off, yes or no, which arrives as a boolean rather than text; a leading zero read as octal; and a two-part version read as a float, where a patch number would change the type. Anchors and merge keys are refused with the line.