SilverStripe and a few other frameworks use a variant of standard HTML comments within their template engines. This enables the engine to easily strip out comments before sending the page to the client, but it does cause an issue for most syntax highlighting text editors. Since Sublime Text 2 is my editor of choice, heres a simple Gist to make it syntax highlight these comments correctly. Add the above excerpt to HTML/HTML.tmLanguage in your Sublime Text 2 Packages directory.