anchor.diff:  * `View` - identifies a view description; subsumed by `Enum_choice`.
   
   
  -## Field value types
  +== Field value types
   
   Field value types are identified by URIs or CURIEs that are used to identify some value type.
   
  
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  ## References
  
  1. [Foundation responsive web framwork](http://foundation.zurb.com)
  
  2. [Foundation grid](http://foundation.zurb.com/docs/components/grid.html)
  
  3. [CURIE](http://www.w3.org/TR/curie/)
  
  4. [URI](https://tools.ietf.org/html/rfc3986)
  
  
  
  
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  Default placement can be specified as part of the field description, and overridden when the field is included in a particular view.
  
  === Placeholder (`Field_placeholder`)
  
  A string that is presented to describe the expected field content when the field content is empty
  
  === Property (`Field_property`)
  
  A http://www.w3.org/TR/curie/[CURIE] or https://tools.ietf.org/html/rfc3986[URI] that is used to relate the field value to the containing entity.  The supplied string is used as a key value in the stored JSON.  The use of CURIE or URI formats for this key allows Annalist data to be interpreted as JSON-LD, hence as http://linkeddata.org[linked data].
  
  A default property CURIE or URI can be specified as part of the field description, and overridden when the field is included in a particular view.
  
  (@@TODO: not yet implemented is management of prefix URIs and JSON-LD contexts required to fully support use as linked data)
  
  === Default (`Field_default`)
  
  A default value for the field if none is specified.
  
  === Enum type (`Field_typeref`)
  
  Used with render types `Enum`, `Enum_optional` and `Enum_choice` (and also `Type`, `List`, `View`, `Field` which are sumsumed by the `Enum*` render types).
  
  When specified, this field value is an internal type identifier.  The field is taken to be a reference to an entity of the given type, and presented for editing as a drop-down list of available values.  For viewing, the field is presented as a hyperlink to a description of the corresponding type.
  
  === Referenced field (`Field_fieldref`)
  
  When a field refers to some target entity, this may indicate a property CURIE or URI for a field of that entity that is used for view rendering.
  
  See section "Resource references, imports and file uploads" for more details.
  
  === Field group (`Field_groupref`)
  
  Field group reference used by `RepeatGroup`, `RepeatGroupRow` and `RefMultifield` renderers.  Otherwise, it is ignored.
  
  