Update syntax for term definition as NCName, and use of Compact IRI o…

…r absolute IRI on the LHS of context.

spec/latest/json-ld-syntax/index.html

@@ -565,9 +565,8 @@ <h3>The Context</h3>
 <p>In JSON-LD, a <tdef>context</tdef> is used to map <tref>term</tref>s, i.e., keys with associated values
   in an JSON document, to <tref>IRI</tref>s. A <tdef>term</tdef> is a short word that MAY be expanded to an
   <tref>IRI</tref>. A <tref>term</tref> MUST have the lexical form of <cite><a
-  href="http://www.w3.org/TR/2009/REC-xml-names-20091208/#NT-NCName">NCName</a></cite> (see [[XML-NAMES]]),
-  an '@' followed by an NCName (other than <code>@context</code>), <tref>compact IRI</tref>, <tref>absolute IRI</tref>, or
-  be an empty string.</p>
+  href="http://www.w3.org/TR/2009/REC-xml-names-20091208/#NT-NCName">NCName</a></cite>
+  (see [[XML-NAMES]]).</p>
 <p>The Web uses <tref title="IRI">IRIs</tref> for unambiguous identification. The
   idea is that these <tref>term</tref>s mean something that may be of use to other developers and that it is useful to
   give them an unambiguous identifier. That is, it is useful for <tref>term</tref>s to expand to IRIs so that
@@ -1798,7 +1797,7 @@ <h3>IRI Expansion Within a Context</h3>
 </pre>
 
 <p>
-<tref>Term</tref>s MAY also be used on the left-hand side of a definition.
+<tref>Term</tref>s, <tref title="compact iri">Compact IRIs</tref> and <tref title="iri">IRIs</tref> MAY also be used on the left-hand side of a definition.
 </p>
 
 <pre class="example" data-transform="updateExample">
@@ -1825,7 +1824,7 @@ <h3>IRI Expansion Within a Context</h3>
 </pre>
 
 <p>
-Note that in this example, the <tref>compact IRI</tref> form is used in two different ways.
+In this example, the <tref>compact IRI</tref> form is used in two different ways.
 The first way, as shown with <code>foaf:age</code> declares both the
 <tref>IRI</tref> for the term (using short-form) as well as the
 <code>@type</code> associated with the <tref>term</tref>. The second way, only
@@ -1836,7 +1835,7 @@ <h3>IRI Expansion Within a Context</h3>
 </p>
 
 <p>
-Full IRIs MAY also be used on the left-hand side of a <tref>context</tref>:
+<tref title="absolute iri">Absolute IRIs</tref> MAY also be used on the left-hand side of a <tref>context</tref>:
 </p>
 
 <pre class="example" data-transform="updateExample">
@@ -1863,7 +1862,7 @@ <h3>IRI Expansion Within a Context</h3>
 </pre>
 
 <p>
-Note that in order for the full IRI to match above, the full IRI MUST also
+In order for the <tref>absolute IRI</tref> to match above, the <tref>absolute IRI</tref> MUST also
 be used in the JSON-LD document. Also note that <code>foaf:homepage</code>
 will not use the <code>{ "@type": "@id" }</code> declaration because
 <code>foaf:homepage</code> is not the same as