Sounds great! Mabye instead of greying it out (which usually indicates that a question is disabled, which it isn't here) use a different color and/or a proper icon, like https://fontawesome.com/v4.7.0/icon/eye-slash

https://github.com/LimeSurvey/LimeSurvey/blob/master/assets/packages/adminpanel/src/components/subcomponents/_questionsgroups.vue#L325

This is a line we have to change.
But first we have to know, how to get the hidden-attribute of a question in vue.js?

@markusfluer: Did you code the side menu? Can you provide a little help and let us know where to start to get the question attribute details for each question so we can check if it is set to be hidden and if this is the case, we need to pass that information into the side menu code so we can add a class like "question-hidden" to the element?

almost done, preparing a pull request

@markusfluer, we will soon send a pull request as discussed at https://www.limesurvey.org/de/foren/development/117180-adminpanel-js-for-pull-request#177978. Could you please review later?

Did I got that correct? Node, npm etc. are becoming part of the LimeSurvey distribution.
Will bring security issue handling to the next level.

For marking hidden questions?
BTW: About hiding questions:
https://bugs.limesurvey.org/view.php?id=11665

again: remember that hidding via CSS or by removing the HTML makes a huge difference in the saved data. Hidden by CSS will be saved has NULL, hidden by removing the HTML will be saved as empty.
any change here will then completely change the habits of survey designer/data analyst.

@LouisGac: We are not planning to change any details at survey runtime. We simply want to add a CSS class to hidden questions listed at the survey tree at the admin backend. The reason for this is that we can then easily mark those hidden questions e.g. by adding some opacity or using grey color.

the change affects the question explorer in backend, which is a vue.js application
therefore adminpanel.js needs to be compiled via gulp

https://github.com/LimeSurvey/LimeSurvey/pull/1198

Hidden question in admin view MUST be seen : please don't use opacity or grey on grey …

And it's always better to have a clean text like we have for error.

Why not adding a clean text in a clean label.

Sample

Capture d’écran du 2019-05-22 12-20-42.png (9,854 bytes)   

Capture d’écran du 2019-05-22 12-20-42.png (9,854 bytes)   

Usage of bg-warning on header (must use bg-danger for EM error)
and label-default for the text

Capture d’écran du 2019-05-22 12-27-46.png (8,445 bytes)   

Capture d’écran du 2019-05-22 12-27-46.png (8,445 bytes)   

@DenisChenu, just for clarification: We are not planning any special design adjustments yet. The goal is to simply add the class and user could then adjust the design details at their own admin theme.

BTW, is the hint about hidden questions at the logic file already available at LS 4 or is this just an example?

Yes: it's an hacked example.

Else : i really think we must

1. Add EM error if we add hidden
2. Never use only css class but text (or data-XXX)
3. Use bootsrap class system

I can make a sample screenshot when i see where younwant to add this : in left menu ? In question overview ? In question list ?

Left menu (survey structure tree) it is.

My opinion : why adding this single information i think iof we add something we have to add

1. Error
2. Have condition
3. Hidden

See screenshot for a sample.

Adding screenshot with only label + screenshoit with some css : bg-danger + bg-warning on draggable with display:table-cell

Capture d’écran du 2019-05-22 15-05-12.png (18,965 bytes)   

Capture d’écran du 2019-05-22 15-05-12.png (18,965 bytes)   

Capture d’écran du 2019-05-22 15-12-54.png (31,373 bytes)   

Capture d’écran du 2019-05-22 15-12-54.png (31,373 bytes)   

Well, for the given use-case we only wanted to mark hidden questions. I am open to discussing how to do that at the next dev meeting. I think we should keep the new class but can extend that. Why not adding small icons for "set to hidden" or "has EM errors" or "uses conditions"? Otherwise, it could be too much text.

Also, feel free to extend the feature to also include details about EM errors and conditions. For the later, would it be possible to not only show a note if the question itself uses conditions but also if follow up questions are conditionally connected to a given question? I assume it is only doable for conditions created by the condition editor but won't work for relevance equations?