Rel JSON Ptr forward/backward index manipulation

This allows using a relative pointer to look ahead or behind
in arrays when calculating the initial point at which to apply
the JSON Pointer that is the suffix of the Relative JSON Pointer.

Author: handrews

relative-json-pointer.xml

@@ -33,7 +33,7 @@
             </address>
         </author>
 
-        <date year="2019"/>
+        <date year="2020"/>
         <workgroup>Internet Engineering Task Force</workgroup>
         <keyword>JSON</keyword>
         <keyword>JavaScript</keyword>
@@ -134,6 +134,24 @@
                     </t>
                 </list>
             </t>
+            <t>
+                If the next character is a plus ("+") or minus ("-"), followed by another
+                continuous sequence of decimal digits, the following steps
+                are taken using the decimal numeric value of that plus or minus sign
+                and decimal sequence:
+                <list>
+                    <t>
+                        If the current referenced value is not an item of an array,
+                        then evaluation fails (see below).
+                    </t>
+                    <t>
+                        If the referenced value is an item of an array, then the
+                        new referenced value is the item of the array indexed by
+                        adding the decimal value (which may be negative), to the
+                        index of the current referenced value.
+                    </t>
+                </list>
+            </t>
             <t>
                 If the remainder of the Relative JSON Pointer is a JSON Pointer, then
                 evaluation proceeds as per
@@ -300,6 +318,11 @@
             </t>
             <t>
                 <list style="hanging">
+                    <t hangText="draft-handrews-relative-json-pointer-03">
+                        <list style="symbols">
+                            <t>Add array forward and backward index manipulation</t>
+                        </list>
+                    </t>
                     <t hangText="draft-handrews-relative-json-pointer-02">
                         <list style="symbols">
                             <t>Update to the latest JSON RFC</t>