view.extract_completions() is case sensitive but the standard completion is case insensitive:
setBoxReadOnly
|
setb -> TAB -> setBoxReadOnly
view.extract_completions('setb') -> ]
view.extract_completions('setB') -> 'setBoxReadOnly']
IMHO a new argument to select case sensitivity is the best solution, if not possible, make extract_completions case insensitive.