textdata may be any arbitrary UTF-8 string. If the key is not present, the empty string must be returned.
"ricmoo.eth"could set this to
.io, etc) or ENS name (i.e.
.eth). Service Keys must contain at least one dot.
TXTrecords, which allow for a general keys and values, allowing future extension without adjusting the resolver, while allowing applications to use custom keys for their own purposes.