This is a simple set of properties that can be shared across many simple 
applications.

~~~ ~usage~ A descriptive note giving examples of how a descriptor 
         should be used.
         
~~~ ~content~ Constraints and instructions on the value for a specific 
         descriptor.
         
~~~ ~url~ The value contains a url for the parent attribute.

~~~ ~id~ The identifier for the description or part of a description. The 
         description identifier must be unique within at least the service 
         providing the description. A descriptor identifier must be unique 
         within the text stream.
         ~usage~
|             ~id~ identifer
|             Item~ 
|                 ~id~ item1
|                 title~ Hamlet
|                 etc~            

~~~ ~service~ A partial url which when containing the identifier provides 
         access to the description. The position of the identifier is marked 
         by {identifier}. An external reference to a specific 
         descriptor within the text stream comprises the ~id~ of descriptor 
         appended to the text stream ~id~ as follows :
                {text stream ~id~}#{descriptor ~id~}
         A text stream may be provided by more a than one service so there 
         may be several values for this. 
         ~usage~
|             ~id~ identifer
|             ~service~ Oldieshome example service
|                 ~url~  https://oldieshome.org.uk/descriptions?id={identifier}    

~~~ ~created~ The value is the date and time the description was first created.
        ~content~ All date and time properties should use the same format based on 
        ISO ???? .  

~~~ ~updated~ The value is the date and time the description was updated.

~~~ ~version~ A version number or statement for description.

~~~ ~language~ The language used in the text stream. This is not the 
        same as the language appearing in the entities described in
        the text stream. Use language~ for that purpose. 
        The value may be either the code or 
        the language name specified in ????.

~~~ ~note~ A note about the act of creating or updating a descriptor, the 
        value's source and some specific aspect of the value.
         
~~~ ~by~ The person or other agent responsible for an action.
    ~usage~ For example associated with an update :
|             ~updated~ 2019-08-31T10:37:56
|                 ~by~ Bill Oldroyd
|                 ~note~ Correcting spelling mistakes