I can't understand which action I need to take when I find this message:
This happens when I press Ctrl+F12 to see the visual editor.
Previously it worked well because I have assigned an HTML code to this form, but suddenly it shows this message.
OK.
I discovered how to react to this message.
This message, obviously, means that this form is visually inherited from TscCustomWebForm.
You need to open TscCustomWebForm in design mode with Ctrl+F12.
After that, you do the same with the TUsersForm, and the TUserForm design will replace the TscCustomWebForm design in VSC.
It is not very intuitive, but at least It works.
Please, ensure all your forms are included in the .dproj, that is, are added to the project, if not, when opening a form that inherits from another form, the form designer is not able to open the base forms. This works the same way in RAD Studio.
I'm working simultaneously with both environments: Delphi IDE and VSC.
Of course, all the forms are included. However, in the case of visual inheritance, the VSC designer cannot locate the parent design.
You need to open the parent form, click Ctrl+F12 to show the designer and repeat this action with the inherited form you want to edit.
The inherited design will be substituted in the VSC for the parent design.
If at some point you can send me the project or a way to reproduce your issue, I can take a look to find out what is going on. Thanks!
I've discovered the misunderstanding.
In VSC, you can only have ONE tab for Design.
If you try to open a DFM that is visually inherited from another in the Designer Tab, you need to open first the parent one.
One time you have opened the original form, you can open in different sub-tabs of the Design Tab, as many descendants of it as you want.