XML

From APIDesign

The wikipedia::XML language is unique when it comes to BackwardCompatibility as it requires each document to encode the version of the used XML dialect as its first line. Each document starts with:

<?xml version="1.0"?>
<!-- or -->
<?xml version="1.1"?>

as a result by parsing the first line, each parser knows what rules to apply to the rest of the document.

Should all languages specify their version as soon as possible, we wouldn't see the Python 2.x vs. 3.0 problem!