Extension of original HTML syntax to support grit preprocessor <if expr="...">...</if> blocks.
<if expr="False"> blocks have special handling in that they are shown as visually disabled.
Open HTML file and set the HTML (+Grit) syntax for it.
It's recommended to use Open all with current extension as... option so that this syntax
is automatically applied to all HTML files.
Due to original syntax being referenced from this one, all updates to original one will automatically be included so it's safe to just use this syntax for all HTML files.