- HTML-escape double quotes as " in backtick template literals for valid attribute values
- Merge shorthand classes (.alert) with class attribute values instead of emitting duplicates
- Handle string concatenation expressions in class attributes (e.g., class="btn btn-" + type)
When a mixin calls another mixin passing a variable with the same name
as the parameter (e.g., +alert(message) where alert has param message),
skip generating redundant const declaration since the variable is already
in scope.
Also adds missing alert.pug mixin for demo project.
