Script execution is standard in modern ajax engines like rich, ice or fry.
If a piece of XHTML comes in via xhr and contains <script> tags the ajax engine
should automatically trigger execution of these scripts. This is important if
you want to replace a js function or if the scripts somehow initialize UI
elements. It depends on a combination of the js replacement code
(innerHTML/adjacentHTML/contextualFragment/...) and the browser platform whether
the browsers automatically run these scripts, IE mostly doesn't run them FF
mostly does so. The ajax engine should know whether the browser does
automatically run the scripts and if it doesn't they should be triggered via js.