enable exclusion queries

[aappling-usgs]

ScienceBase lets you explicitly exclude items that match criteria; see "Exclude Elements in Search Results" in https://www.sciencebase.gov/about/content/sciencebase-advanced-search. It would be great if this were also possible through sbtools, but if it is already possible, I can't figure out how to do it.

Using my browser directly,
https://www.sciencebase.gov/catalog/items?q=&lq=flood%20AND%20earthquake currently returns 62 results while
https://www.sciencebase.gov/catalog/items?q=&lq=flood%20AND%20earthquake&filter=browseCategory!%3DPublication returns 7 results

Using sbtools, I don't know how to get my 7 results. Here's what I can get:

> length(query_sb(query_list = list(q = '', lq = 'flood AND earthquake'), limit=100))
[1] 62
> length(query_sb(query_list = list(q = '', lq = 'flood AND earthquake', 'browseCategory' = "Publication"), limit=100))
[1] 55
> length(query_sb(query_list = list(q = '', lq = 'flood AND earthquake', 'browseCategory!' = "Publication"), limit=100))
[1] 62
> length(query_sb(query_list = list(q = '', lq = 'flood AND earthquake', 'browseCategory' = "!Publication"), limit=100))
[1] 0

The 3rd and 4th queries above get converted into these URLs within httr::GET:
query_sb(query_list = list(q = '', lq = 'flood AND earthquake', 'browseCategory!' = "Publication"), limit=100) -> https://www.sciencebase.gov/catalog/items/?q=&lq=flood%20AND%20earthquake&browseCategory%21=Publication&s=Search&format=json&fields=id%2Ctitle%2CparentId%2CdateCreated%2ClastUpdated%2CcreatedBy%2ClastUpdatedBy%2Cfiles&max=100
query_sb(query_list = list(q = '', lq = 'flood AND earthquake', 'browseCategory' = "!Publication") -> https://www.sciencebase.gov/catalog/items/?q=&lq=flood%20AND%20earthquake&s=Search&format=json&fields=id%2Ctitle%2CparentId%2CdateCreated%2ClastUpdated%2CcreatedBy%2ClastUpdatedBy%2Cfiles&max=100&filter=browseCategory%3D%21Publication

It appears that the ! comes closest to the right position with 'browseCategory!'=..., but it gets converted into %21 and so loses its intended effect.

So. Is exclusion already possible using some other syntax? If not, could it be made possible?