Mohammad,
If I may explain the Qualify macro for you in my way.
Just as the <<now>> macro returns the time and date
eg: 10:21, 6th July 2018
The <<qualify>> macro returns a "unique number"
eg: -85796999
and as Jeremy Described "in a way that is unique to the place in the widget tree that it is rendered"
which I may add includes the title, change the title and the result changes.
Now looking at the result returned you can see it is prefixed with a hyphen, this is a clue that you can add another value
<<qualify "mykeyword">>
gives us mykeyword-85796999
Basically it generates on the fly a unique number based on its context which you can use with prefixs to generate more than one for the current context.
It does not matter if the number changes (Like as the title changes) because it reliably returns the same number in the current wiki everywhere it is used.
I suggest when using the <<qualify>> macro to create temp tiddlers <<qualify "$:/temp/mykeyword">>
The world makes a lot of sense (in English), when you think about it, you are asking it to Qualify mykeyword so it is unique in this time and place, so you will not accidentally overwrite or use a temporary tiddler from something else.
Of course this use of the word Qualify may be unfamiliar to many.
Now you may be able to see why it is commonly used for the title of State Tiddlers, this is possibly the only use, however someone may use it in other ways.
Regards
Tony