document functino nr args

docs/language.md

@@ -398,6 +398,8 @@ fn2()               // 1
 
 ### Arguments
 
+Functions can have at most **4 parameters**. Use a record to pass more values.
+
 Extra arguments are ignored. Missing arguments are `null`.
 
 ```javascript
@@ -406,6 +408,11 @@ fn(1, 2, 3)        // 3 (extra arg ignored)
 
 var fn2 = function(a, b) { return a }
 fn2(1)              // 1 (b is null)
+
+// More than 4 parameters — use a record
+var draw = function(shape, opts) {
+  // opts.x, opts.y, opts.color, ...
+}
 ```
 
 ### Immediately Invoked Function Expression