Searches DNS records for a host having the given type. Returns
true if any records are found, and
false if none are found. The host
type can take any of the following values (if no value is specified,
MX is the default):
Start of authority.
Pointer to information.
128-bit IPv6 address.
Defined as part of early IPv6 but downgraded to experimental.
Generalized service location record.
Regular expression based rewriting of domain names.
Originally for human-readable text. However, this record also carries machine-readable data.
Any of the above.
Check http://en.wikipedia.org/wiki/List_of_DNS_record_types for more details.