The differences between XML and HTML are as follows:1. HTML has predefined tags while XML has user-defined tags.2. HTML document can be viewed directly by the Web browser while XML document cannot be viewed directly and need some proper stylesheet files.A well-formed document means to follow several generic rules, such as follows:1. XML document must contain at least one element.2. All tags must have the opening and closing tags as these XML tags are case sensitive.The XML code is<?xml version = '1.0' encoding = 'UTF-8'?><Travels> <Travel><Designation> Singapore </Designation><Cost> 200000 </Cost><No_of_days> 8 </No_of_days><Mode_of_trans> Aeroplane </Mode_of_trans></Travel></Travel><Designation>Shimla</Designation><Cost> 10000 </Cost><No_of_days> 4</No_of_days><Mode_of_trans> Bus </Mode_of_trans></Travel></Travels>