Object fields get the tag !nim:field. Fixes #12.

doc/index.txt

@@ -252,11 +252,11 @@ Defining a custom tag uri for a type
   </td><td>
 
 .. code-block:: yaml
-  %YAML 1.2
+  YAML 1.2
   --- !Mob
-  !!str level: !nim:system:int32 42
-  !!str experience: !nim:system:int32 1800
-  !!str drops: !Drops [!!str Sword of Mob Slaying]
+  !nim:field level: !nim:system:int32 42
+  !nim:field experience: !nim:system:int32 1800
+  !nim:field drops: !Drops [!!str Sword of Mob Slaying]
 
 .. raw:: html
   </td></tr></tbody></table>

private/serialization.nim

@@ -341,8 +341,9 @@ proc representObject*[O: object|tuple](value: O, ts: TagStyle,
         let childTagStyle = if ts == tsRootOnly: tsNone else: ts
         yield startMapEvent(tag, yAnchorNone)
         for name, value in fieldPairs(value):
-            yield scalarEvent(name, presentTag(string, childTagStyle),
-                              yAnchorNone)
+            yield scalarEvent(name,
+                    if childTagStyle == tsNone: yTagQuestionMark else:
+                    yTagNimField, yAnchorNone)
             var events = representChild(value, childTagStyle, c)
             while true:
                 let event = events()

private/tagLibrary.nim

@@ -23,6 +23,7 @@ proc `$`*(id: TagId): string =
     of yTagTimestamp: "!!timestamp"
     of yTagValue: "!!value"
     of yTagYaml: "!!yaml"
+    of yTagNimField: "!nim:field"
     else: "<" & $cast[int](id) & ">"
 
 proc initTagLibrary*(): TagLibrary =
@@ -76,4 +77,5 @@ proc initSerializationTagLibrary(): TagLibrary =
     result.tags["tag:yaml.org,2002:float"]     = yTagFloat
     result.tags["tag:yaml.org,2002:timestamp"] = yTagTimestamp
     result.tags["tag:yaml.org,2002:value"]     = yTagValue
-    result.tags["tag:yaml.org,2002:binary"]    = yTagBinary
+    result.tags["tag:yaml.org,2002:binary"]    = yTagBinary
+    result.tags["!nim:field"]                  = yTagNimField

yaml.nim

@@ -376,6 +376,10 @@ const
     yTagYaml*       : TagId = 16.TagId ## \
         ## `!!yaml <http://yaml.org/type/yaml.html>`_ tag
     
+    yTagNimField*   : TagId = 100.TagId ## \
+        ## This tag is used in serialization for the name of a field of an
+        ## object. It may contain any string scalar that is a valid Nim symbol.
+    
     yFirstCustomTagId* : TagId = 1000.TagId ## \
         ## The first ``TagId`` which should be assigned to an URI that does not
         ## exist in the ``YamlTagLibrary`` which is used for parsing.