




Calls the completion-function in a text-input-pane.
The function text-input-pane-complete-text calls the 
completion-function
 of 
pane
 with the current 
text
. If this call is successful, then the 
text
 of 
pane
 is set to the result, and text-input-pane-complete-text returns this result. Otherwise, 
result
 is 
nil
.
Note: the completion-function may return a list of completion candidates, in which case text-input-pane-complete-text will prompt the user to select one of the candidates.