Help is not showing for 100% clearly known method

Typical workflow:
Write
QString s; s.res
Popup will appear and you select "reserve" and hit ENTER. And get the code:
QString s; s.reserve(<cursor>)
And there will be small window wich shows that there is only one modification of method reserve. If you press F1 you will get Help window saying "No documentation available."
But why? There is only one available method with such name in Qstring class! So why it is necessary to require people to input all params accoding to method definition to get help for this method?

Moreover in most cases I need help just to fill in the parameters ... but to get the help QtCreator asks me to fill params! But what if there are many of them?