On xwiki 6.3, when we edit a scheduled job, inline mode is open and we can modify "job script" emplacement but on xwiki 6.4 "job script" is read only and don't display the groovy code.
On Xwiki 6.4 we must open schedule job page in "edit mode" to have the normal screen to edit all the field (and display the help "The script is the code that will be executed when the job is triggered by the scheduler. It should be written in the Groovy language. ....").
Tested on my xwiki plateform and new jetty standalone package