There may be times when you do not wish to exclude [tokens with] a factor from your entire analysis, but you do want to exclude [that factor] from the results of a given factor group. - Goldvarb 2001 Users' Manual
Since Rbrul was created in 2008, users have asked about the possibility of this type of partial exclusion. Until now, this capability has continued to be available only in Goldvarb. While Goldvarb is still the only way to achieve more complex exclusions (for example, excluding tokens from the results of one factor group based on the values of another factor group), Rbrul now emulates the Goldvarb "slash operator" in its primary usage.
If one or more tokens have "/" (slash) for a certain predictor (factor group), then regardless of the value(s) of the dependent variable for those tokens, the log-odds coefficient for the slashed group is forced to zero (factor weight .500), although this is reported as "NA" for the sake of clarity. In effect, these tokens are ignored in the calculation of the other results for that predictor, while being included normally in the calculations for the other predictors.
I have not tested this new function very thoroughly, only making sure that the output matched Goldvarb on a few simple models. So please give me feedback (firstname.lastname@example.org) if it seems to have problems, or even if it seems to be working properly.
Thanks for your patience, and happy slashing!