Add fragment to YAML format

_pages/yaml-file-format.md

@@ -99,7 +99,14 @@ Three keys are always present:
     </tbody></table>
 
     The URI that identifies the concept documented in this YAML file.
-
+    If the YAML file also includes the key <code>fragment</code>,
+    this URI should be followed by a fragment identifier when used;
+    the meaning of the fragment is defined by the <code>fragment</code> entry.
+
+    For example, if <code>uri</code> is "https://gedcom.io/terms/v7/RIN" and
+    <code>fragment</code> is "Source System", then a full URI might be
+    "https://gedcom.io/terms/v7/RIN#MyProgram" where the fragment identifier
+    "MyProgram" indicates the source system that generated the RIN payload value.
 ## Other keys
 
 The following keys may appear in a YAML file.
@@ -184,6 +191,19 @@ Their names may be changed a YAML file with a `lang` other than `en`.
     Standard structures may have an `extension tags` entry to list *fully compatible* extensions that predated the standard and can be converted to the `standard tag` without any other modification.
     For example, 7.0's `UID` structure is fully compatible with the common 5.5.1 extension identified by tag `_UID`.
 
+-   <table><tbody>
+    <tr><th>Key</th><td><code>fragment</code></td></tr>
+    <tr><th>Type</th><td><code>str</code></td></tr>
+    <tr><th>Required by</th><td>—</td></tr>
+    <tr><th>Allowed by</th><td><code>type: uri</code></td></tr>
+    </tbody></table>
+
+A recommended brief name or label for a fragment identifier, to show to users. Labels are user-centric; for programmer-centric explanations of the concept, see `specification`.
+
+Labels are short to fit in forms and other constrained-space UI elements; for more detailed text see `help text`.
+
+    By being present in the YAML file, this field also implies that the URI should have a fragment identifier appended to it when used.
+
 -   <table><tbody>
     <tr><th>Key</th><td><code>help text</code></td></tr>
     <tr><th>Type</th><td><code>str</code></td></tr>