Is there a special header structure required for text classification problems?I'm trying to do Tweet classification using the text mining plugin. I have the data in a CSV file, with one column labeled category and containing my two categories, and the other labeled text containing the tweets. When I load the file with the corpus widget and follow the workflow given at http://orange3-text.readthedocs.io/en/latest/widgets/bagofwords.html the test widget gives the error Train data input requires a class variable.I opened the sample bookexcerpts.tab data and discovered it has a different header structure than just category and text.  If I modify my tweet CSV to match it seems to work. Is this a bug, or am I missing a step?
Orange Text Mining Data Format
text mining;orange