CommandEntry is usable, but not everything works as of yet:
 - SyntaxHighlighting is crippled. It does not work in Maxima, but
   in Qalculate some things are highlighted.
 - Completion does not work, because Tabs are not recognised.
 - The WorksheetTextItems do not look nice: They have a wierd border,
   and the cursor is not shown.
 - WorksheetTextItems are also too small, they should fill the whole
   line.
 - Cursor movement does not work for additional information blocks.
   But I am not sure whether one should be able to navigate out of
   those, as any modification outside should abort the evaluation
   and destroy the additional information.
 - There most certainly is more.
Other Entries can not yet be added to the Worksheet.