However, in other cases the presence of a rule violation in ones code can be a red flag that something can go seriously awry at runtime, even if the compiler lets it slip by.

The style sheet compiler therefore constructs a decision tree which is used at run time to decide which template rule to apply to a given node.

If you relax the type-conversion rule, the compiler operates under permissive type semantics, which allows you to make narrowing conversions without conversion keywords.