+STR
+DOC
+MAP
=VAL :foo
+SEQ <tag:yaml.org,2002:seq>
=VAL <tag:yaml.org,2002:str> :a
+MAP <tag:yaml.org,2002:map>
=VAL :key
=VAL <tag:yaml.org,2002:str> :value
-MAP
-SEQ
-MAP
-DOC
-STR