Identifying non-data columns

In one of the recent bayestestR PRs (https://github.com/easystats/bayestestR/pull/673 & https://github.com/easystats/bayestestR/pull/672) some of the printing methods have adopted allowing for arbitrary columns in the resulting data frame objects. This was done by setting a new type of attribute called idvars the contained the names of the columns that don't hold the "statistical" information, but information used to identify the rows.

I've found this to better and more stable than keeping track of all possible column names, and very flexible.

I wonder if this should be used across easystats? We can have several "classes" of such attributes - idvars, grouping-vars, etc....

These could be useful if "detected" by the various formatting and printing methods in parameters (which is why I've opened this issue here, but feel free to move it elsewhere) and in insight (maybe also datawizard, correlation and modelbased?).

WDYT? @easystats/core-team

Start by reviewing the referenced bayestestR pull requests and the printing methods in parameters that handle data-frame columns. Then inspect related formatting methods in insight and the other mentioned packages to determine whether a shared attribute convention is feasible. Done means the scope and attribute design are agreed across the relevant packages.