Edit documentation.

doc/src/language/functions.md

@@ -18,6 +18,7 @@ print(add(2, 3));   // prints 5
 print(sub(2, 3,));  // prints -1 - trailing comma in arguments list is OK
 ```
 
+
 Implicit Return
 ---------------
 
@@ -38,6 +39,7 @@ print(add(2, 3));   // prints 5
 print(add2(42));    // prints 44
 ```
 
+
 No Access to External Scope
 --------------------------
 
@@ -50,13 +52,15 @@ let x = 42;
 fn foo() { x }      // <- syntax error: variable 'x' doesn't exist
 ```
 
-Passing Arguments by Value
--------------------------
+
+Arguments Passed by Value
+------------------------
 
 Functions defined in script always take [`Dynamic`] parameters (i.e. the parameter can be of any type).
-It is important to remember that all arguments are passed by _value_, so all functions are _pure_
-(i.e. they never modify their arguments).
+Therefore, functions with the same name and same _number_ of parameters are equivalent.
 
+It is important to remember that all arguments are passed by _value_, so all Rhai script-defined functions
+are _pure_ (i.e. they never modify their arguments).
 Any update to an argument will **not** be reflected back to the caller.
 
 This can introduce subtle bugs, if not careful, especially when using the _method-call_ style.
@@ -71,6 +75,7 @@ x.change();         // de-sugars to 'change(x)'
 x == 500;           // 'x' is NOT changed!
 ```
 
+
 Global Definitions Only
 ----------------------
 
@@ -92,6 +97,12 @@ fn do_addition(x) {
 }
 ```
 
-Unlike C/C++, functions can be defined _anywhere_ within the global level. A function does not need to be defined
-prior to being used in a script; a statement in the script can freely call a function defined afterwards.
-This is similar to Rust and many other modern languages.
+
+Use Before Definition
+--------------------
+
+Unlike C/C++, functions in Rhai can be defined _anywhere_ at global level.
+A function does not need to be defined prior to being used in a script;
+a statement in the script can freely call a function defined afterwards.
+
+This is similar to Rust and many other modern languages, such as JS's `function` keyword.