RTC 6.0.2 custom attributes
One answer
For all I know, this is not possible without heavy, expensive customization, if possible at all.
Comments
I am sure the functionality existed on the version before 4.0.x
The attribute called discussion has the same behavior too.
I am working on RTC since 12 years and there has never been anything like this.
Discussion is not an attribute but a collection of comments with a very special presentation.
You can make attributes read only using operational behavior and conditions as well as in the editor presentation, but such an attribute will only ever be one text attribute and if read only it is completely read only and not what you asked for.