Always use "hostname" for formats.

Use "idn-hostname" instead of "idn", and since "hostname" did
not talk about ___domain names, remove discussion of ___domain names
from the updated description.

Author: handrews

jsonschema-validation.xml

@@ -973,25 +973,27 @@
                         valid against the "idn-email" attribute.
                     </t>
                 </section>
-                <section title="Host and ___domain names">
+                <section title="Hostnames">
                     <t>
                         These attributes apply to string instances.
                     </t>
                     <t>
                         A string instance is valid against these attributes if it is a valid
-                        representation for an Internet host name as follows:
+                        representation for an Internet hostname as follows:
                         <list style="hanging">
                             <t hangText="hostname">
                                 As defined by <xref target="RFC1034">RFC 1034, section 3.1</xref>,
                                 including host names produced using the Punycode algorithm
                                 specified in <xref target="RFC5891">RFC 5891, section 4.4</xref>.
                             </t>
-                            <t hangText="idn">
+                            <t hangText="idn-hostname">
                                 As defined by either RFC 1034 as for hostname, or an
-                                internationalized ___domain name as defined by
+                                internationalized hostname as defined by
                                 <xref target="RFC5890">RFC 5890, section 2.3.2.3</xref>.
                             </t>
                         </list>
+                        Note that all strings valid against the "hostname" attribute are also
+                        valid against the "idn-hostname" attribute.
                     </t>
                 </section>