🐐 String interpolation

README.md

@@ -65,6 +65,21 @@ Strings are concatenated with `&`:
 
 `NVLLVS` coerces to an empty string when used with `&`. Note: `+` is for arithmetic only — using it on strings raises an error.
 
+#### String Interpolation
+
+Double-quoted strings support interpolation with `{expression}`:
+
+```
+DESIGNA nomen VT "Marcus"
+DICE("Salve, {nomen}!")        // → Salve, Marcus!
+DICE("Sum: {III + IV}")        // → Sum: VII
+DICE("{nomen} has {V} cats")   // → Marcus has V cats
+```
+
+Any expression can appear inside `{}`. Values are coerced to strings the same way as with `&` (integers become Roman numerals, booleans become `VERITAS`/`FALSITAS`, etc.).
+
+Single-quoted strings do **not** interpolate — `'{nomen}'` is the literal text `{nomen}`. Use `{{` and `}}` for literal braces in double-quoted strings: `"use {{braces}}"` → `use {braces}`.
+
 Integer modulo is `RELIQVVM`: `VII RELIQVVM III` evaluates to `I`. Under the `FRACTIO` module it returns a fraction, so `IIIS RELIQVVM IS` is `S` (i.e. 1/2).
 
 ### Integers