This is actually a problem with a lot of languages that allow runtime template like String interpolation. For example Groovy on the JVM has GStrings which one

This is actually a problem with a lot of languages that allow runtime template like String interpolation. For example Groovy on the JVM has GStrings which one can do fairly nasty things. As well it actually is fairly hard to lock down most of the template languages on the JVM for user templates. (If you are going to allow user templates I recommend one of the Java Mustache-like implementations).