You might be interested in storing your data in a changing format. XML definitely allows that - being able to define your own tags at will is somewhat akin to being able to add and remove columns without migrating data.
XML can remove the usage of a database - but as the size of the XML file grows, lookup and search become ever more costly. For a personal content management system - especially one where you are looking at the beginning of a file in your most common use case - it could be an acceptable solution.
Making a CMS like this would be something like using TiddlyWiki, which is a single html file that hosts an entire wiki.
For even slightly larger scale CMS, I would immediately opt for a database - probably SQLite for smaller scale, because it's the thing to do nowadays.