In Flash Builder 4.0, by default, context-sensitive Help in Flash Builder for items in the ActionScript Language Reference (ASLR) doesn't work. Instead, it displays the Using Flash Builder home page. See bug FB-26153 for more information,
To enable context-sensitive Help for the ASLR, use the CHC to download Help to your local system. Choose Edit > Preferences from the menu bar.
In this release, the CHC does not prompt you to download a local version of Help upon first invocation. However, it does prompt you to download local Help on subsequent invocations.
You can download a local version by using the CHC preferences panel by choosing Edit > Preferences. Or, you can access Help a second time, which then displays the download prompt.