in content/resources/js/prettify.js [1187:1196]
function langHandlerForExtension(extension, source) {
if (!(extension && langHandlerRegistry.hasOwnProperty(extension))) {
// Treat it as markup if the first non whitespace character is a < and
// the last non-whitespace character is a >.
extension = /^\s*</.test(source)
? 'default-markup'
: 'default-code';
}
return langHandlerRegistry[extension];
}