tld_extract extracts the top-level domain (TLD) from
a vector of domain names. This is distinct from the suffixes, extracted with
suffix_extract; TLDs are top level, while suffixes are just
domains through which internet users can publicly register domains (the difference
between .org.uk and .uk).
# NOT RUN {# Using the inbuilt datasetdomains <- domain("https://en.wikipedia.org/wiki/Main_Page")
tld_extract(domains)
# Using a refreshed onetld_extract(domains, tld_refresh())
# }