What exactly happens when Complex Script Support is enabled?

Question

When we click the check box "Install files for complex script and right to left languages (including Thai)" in Regional and Language settings what exactly happens?

1. Changes to registry keys?
2. I noticed that it installs some .fon files and keyboard dlls.

Is this totally necessary if one just wish to read complex script on Windows XP? My test inside VirutalBox as Windows 7 as the host OS seems to indicate that for reading Complex Script need not be enabled. Yet that's not what all the literature on the subject says. What's going on?

Update: http://hi.wikipedia.org should not be readable if Complex Script is not enabled: http://hi.wikipedia.org/wiki/विकिपीडिया:Devanagari_Help

Problem is that it is readable.

Answer 1

Font files. Rendering libraries ('Uniscript'). Input methods. Certainment beaucoup de cle-registry. (Certainly lots-o-registry-keys.)

Note that IE will tend to get things right even when other things don't, since it builds in a good deal of fancy-pants rendering. Try, oh, Outlook, or some simple sample Win32 program.