added conditional compilation.

doc/ref.html

@@ -1416,7 +1416,7 @@ type is bound to the iterator type. It can still be accessible after the iterati
 </p>
 
 <pre>
-    <k>var</k> a : Array&lt;Int&gt; = ["hello","world","I","love","haXe","!"];
+    <k>var</k> a : Array&lt;String&gt; = ["hello","world","I","love","haXe","!"];
     <k>for</k> txt <k>in</k> a {
         tf.text += txt + " ";
     }
@@ -1426,6 +1426,44 @@ type is bound to the iterator type. It can still be accessible after the iterati
 	This sample will build the string by listing an array elements using an iterator. It is same as calling <code>a.iterator()</code> in the <code>for</code> expression.
 </p>
 
+<a name="cond"></a>
+<h2>Conditional Compilation</h2>
+
+<p>
+	Sometimes you might want to have a single library using specific API depending on the platform it is compiled on. At some other time, you might want to do some optimizations only if you turn a flag ON. For all that, you can use <em>conditional compilation macros</em> :
+</p>
+
+<p>
+	Here's an example of multiplaform code :
+</p>
+
+<pre>
+    #flash8
+    <g>// specific flash 8 code</g>
+    #else flash
+    <g>// generic flash code</g>
+    #else js
+    <g>// javascript specific code</g>
+    #else neko
+    <g>// neko specific code</g>
+    #else error <g>// will display an error "Not implemented on this platform"</g>
+    #end
+</pre>
+
+<p>
+	Here's another example for turning on some logs only if <code>mydebug</code> flag is used when compiling the code :
+</p>
+
+<pre>
+    #mydebug
+    trace("Some debug infos");
+    #end
+</pre>
+
+<p>
+	You can define your own variables by using the <b>haXe</b> compiler commandline options.
+</p>
+
 <h2>And Now ?</h2>
 
 <p>