Add note on &T parameters.

doc/src/language/method.md

@@ -36,6 +36,8 @@ update(array[0]);   // <- 'array[0]' is an expression returning a calculated val
 array[0].update();  // <- call in method-call style will update 'a'
 ```
 
+**IMPORTANT: Rhai does NOT support normal references (i.e. `&T`) as parameters.**
+
 
 Number of Parameters
 --------------------
@@ -51,8 +53,8 @@ The following table illustrates the differences:
 |  Rhai script  |    _n_     |         `this`         |                  `fn method(x, y) {}`                   |
 
 
-`&mut` is Efficient (Except for `ImmutableString`)
+`&mut` is Efficient, Except for `ImmutableString`
-------------------------------------------------
+-----------------------------------------------
 
 Using a `&mut` first parameter is highly encouraged when using types that are expensive to clone,
 even when the intention is not to mutate that argument, because it avoids cloning that argument value.

doc/src/rust/custom.md

@@ -83,6 +83,8 @@ engine
 ***Note**: Rhai follows the convention that methods of custom types take a `&mut` first parameter
 so that invoking methods can update the types. All other parameters in Rhai are passed by value (i.e. clones).*
 
+**IMPORTANT: Rhai does NOT support normal references (i.e. `&T`) as parameters.**
+
 Use the Custom Type in Scripts
 -----------------------------
 
@@ -125,8 +127,8 @@ Under [`no_object`], however, the _method_ style of function calls
 let result = engine.eval::<()>("let x = [1, 2, 3]; x.clear()")?;
 ```
 
-[`type_of()`]
+`type_of()` a Custom Type
--------------
+-------------------------
 
 [`type_of()`] works fine with custom types and returns the name of the type.
 

doc/src/rust/getters-setters.md

@@ -42,3 +42,5 @@ let result = engine.eval::<String>(r#"let a = new_ts(); a.xyz = "42"; a.xyz"#)?;
 
 println!("Answer: {}", result);                     // prints 42
 ```
+
+**IMPORTANT: Rhai does NOT support normal references (i.e. `&T`) as parameters.**