QML import statement: why specify module version?

Question

I know what version of Qt I'm shipping my app with. And I suppose a single version of Qt contains only a single version of each QML module. So if I were to write:

import QtQuick

(no version specified), that would be unambiguous. So why is it necessary to specify the module version?

Answer 1

It is, so everyone can see, which version is demanded.

It might be that you ship your code, using features of QtQuick 2.7, someone tries to open it with an older version (say: QtQuick 2.5) and strangely - it's broken.
If you import a specific version, it is clear, that the error stems from an too old version.

I think it is the best to always try to use the least version. So unless you use features of QtQuick 2.7, declare the older ones, to maximize compatibility.