What is this template ?

This is a feature request. There is no Limesurvey template shown on the screenshot.

Oups ..... sorry :)

Then : for "slider unset" :

• extra place (this feature)
• At left (or right for RTL language)
• At middle

Right ?

You're thinking inside the current LS 2.5 question structure, right?
Sounds valid to me. But for LS 3.0 more (slider) question types with less options will help to keep code and usage easy.

-1 0 ---50/51--- 100 101

For LTR Language
With allowing to put slider in region -1 or 101 you could define
e.g. region -1 = start position of slider (question not touched, which will be a different beast when start position is 50/51=middle)
region 101 = Position to put slider when you don't want to answer the slider question.

For LS 3.0 more of the same question types with a few different options.
There isn't only one slider concept for questions. When you start the sliders in the middle it is a different concept. The reset button gets useful, since you cannot put the no answer and not touched position on 50/51 without a reset button.

Maybe : if default position is set to '' => don't show the slider-handle ?

PS : for LS3 : you can set 0 to default value (or anything you want inside slider min/max) but DON'T set value.

My opinion : QuestionTheme , no need a new settings.

We already have the "reset" button : https://demo.sondages.me/99881?newtest=Y#

I have run into a need for this as well. The “Reset” button doesn't help here, because there is a need to distinguish between null and the default answer. If I have a default of 0, hitting reset will restore 0, but it leaves me with no way to distinguish between a real 0 and an “I don’t know”, which was the context of the original request from Elfrhadwrmai_199921 for this. I would find it useful as well.