Ensure all values to be changed are wrapped in placeholders

aux/placeholder.typ

@@ -14,3 +14,15 @@
     }
   )
 }
+
+// rawPlaceholder returns the very same value and type without altering it.
+// Has the ability to panic if panicOnPlaceholder is set to true.
+#let rawPlaceholder(value) = {
+  context(
+    if panicOnPlaceholder.get() {
+      panic("Found placeholder and panicOnPlaceholder is set.")
+    }
+  )
+
+  return value
+}