bing                    Search Bing
crossref                Find DOI's and other bibliographic metadata
duckduckgo              Search Duckduckgo
github                  Search GitHub
google                  Search Google
google_scholar          Search Google Scholar
qwant                   Search Qwant
r_bloggers              Search r-bloggers.com
rdocumentation          Search rdocumentation.org
rdrr_io                 Search rdrr.io
reddit                  Search Reddit
stackoverflow           Search Stackoverflow
twitter                 Search Twitter
web                     Access Domain
wikipedia               Search Wikipedia
wolframalpha            Search WolframAlpha
