Why are many users comfortable working with XML files?

Users find XML files comfortable to work with primarily because they share the same syntax as HTML. This familiar syntax leads to an easier onboarding experience for those who have worked with HTML, as many of the structural concepts are similar, such as the use of tags to define elements. Additionally, since HTML and XML both utilize a hierarchical structure, individuals with knowledge of HTML can more readily understand and manipulate XML data.

The familiarity with markup languages allows users to quickly grasp how to format data, which makes XML accessible to a wider range of users, including those who may not have extensive programming backgrounds. This universality in syntax helps facilitate the integration of XML into various applications and services, further enhancing its appeal.

The other choices reflect some characteristics of XML files but do not capture the primary reason behind users' comfort. While XML is a universally accepted format, that acceptance does not inherently translate to user comfort without prior experience. Although parsing XML can be easier in some contexts, this is not universally true. Furthermore, XML is not a proprietary format; it is an open standard, which means that its non-propriety also supports widespread user comfort, but it does not provide the same level of familiarity that sharing syntax with HTML does.