November 10th Reading Notes

XML, as I understand it, is a format that one can use to manipulate the placement of documents and entities on a webpage that might be difficult or require additional software when using HTML. It allows the use of graphics and accompanying comments, as one example. I don ot fully understand how XML does this and why HTML does not. I am also confused about the different schema that goes along with XML. It seems like these different schema are needed to do things that one cannot do under normal HTML or XML format. It also seems like they come as addition software or something similar. How do all these languages work together and why can they not be combined as one?