How to enable autocomplete/syntax-highlight for PHP core functions in Eclipse?

I searched a lot, checked many times the neccesary steps, but it still don't work.

My environment is :

1. Latest eclipse for PHP developer package

2. Project is newed, not check out directly from SVN

3. .project has a line

   <nature>org.eclipse.php.core.PHPNature</nature>
   

4. .buildpath has a line

   <buildpathentry kind="con" path="org.eclipse.php.core.LANGUAGE"/>
   

5. .settings/org.eclipse.core.resources.prefs has a line

   include_path=0;/projectname
   

6. file ensured opened in PHP Editor

Something works:

1. PHP core function defination displayed when mouse over, and Ctrl+Click will open its defined file, but input 'arr' nothing happens, while a list of array functions expected
2. Autocomplete does work for internal functios/variables such as class members But never works for PHP core functions, neither syntax highlighting