I see. Just the "danger text (red one)" not turns to green color. But I can step the next page.

That sounds like a bug, please file a bug report.

If I've five question and I'd like to one can write different asnwers for every question.

Place something like this in the Question validation equation field for all questions (adjusting the question codes as necessary):
And something like this in the Question validation tip fields:

Dear Lime professionals, I have exactly the same issue is in the topics that opens this thread: how can I set up MINIMUM length for the answers in long and huge text fields.
I have tried the recommended "strlen(this) > 100" in the Question validation equation and id does not work for me.
Could you provide with some further advise on the issue? E.g. Should I replace "this" with any other magic word? What about spaces in the equation? etc...
Thank you very much in advance.
alchv

alchv2018 wrote: I have tried the recommended "strlen(this) > 100" in the Question validation equation and id does not work for me.

Limesurvey version and screenshot of settings (where did you put exactly this setting).

Else : you can use strlen(self) for a single question

Thanks for your quick reply, Denis!

Although it is not clear to me why you suggest putting the equation into "sub-question" line, I have tried it this way and it still does not work for me...

The validation rule you have suggested works great!

But... It does not prevent from the submission of a too short passage. My idea is to request a respondent to write some meaningful text in the field by "imposing" the minimum number of characters for the entered text.

Dear Denis,
Now I have tried your suggested solution for the whole survey preview - it works perfectly and exactly the way I wanted! Thus - many thanks for your great help.
In my previous mail I referred to only the PARTIAL preview of the section instead of the survey as a whole.
Hi life LimeSurvey!
best
alchv