docs(transformer): clarify comment (#7918)

crates/oxc_transformer/src/common/duplicate.rs

@@ -122,7 +122,11 @@ impl<'a> TransformCtx<'a> {
                 let references = create_array(|| expr.clone_in(ctx.ast.allocator));
                 return (expr, references);
             }
-            // Template literal can have no side effects if it has no expressions
+            // Template literal cannot have side effects if it has no expressions.
+            // If it *does* have expressions, but they're all literals, then also cannot have side effects,
+            // but don't bother checking for that as it shouldn't occur in real world code.
+            // Why would you write "`x${9}z`" when you can just write "`x9z`"?
+            // Note: "`x${foo}`" *can* have side effects if `foo` is an object with a `valueOf` method.
             Expression::TemplateLiteral(lit) if lit.expressions.is_empty() => {
                 let references = create_array(|| {
                     ctx.ast.expression_template_literal(