Updated extent.asciidoc

Added example of statistical geography as per #52

Author: archaeogeek

docs/partials/extent.asciidoc

@@ -39,6 +39,7 @@ provided.
 Britain if it only covers England and Wales).
 
 |Comment |
+. This element should be used in preference to a keyword of type "place".
 
 |Examples a|
 * England
@@ -50,6 +51,8 @@ linked data as a gazetteer
 Authority, using GDS "Local authorities in England" as a controlled list
 * http://vocab.nerc.ac.uk/collection/C64/current/5/, Irish Sea, in the
 NERC Vocabulary "C64, United Kingdom Charting Progress 2 sea regions"
+* http://statistics.data.gov.uk/id/statistical-geography/E09000011, Royal 
+Borough of Greenwich ONS Output Area
 
 |Revision date |August 2010
 |===

docs/partials/resourceidentifier.asciidoc

@@ -70,6 +70,7 @@ include this using an Anchor.
 . Implement a preferred presentation method, eg all capitals, and using underscores instead of spaces.
 . Ensure the identifier is web-friendly by using only characters that are un-reserved in URIs or html
 (see https://www.w3.org/Addressing/URL/4_URI_Recommentations.html for more information).
+. Maximise traceability over time by sharing rules for changes and retirement.
 
 |Comment |Since INSPIRE metadata technical guidance version 2, it is no longer required to use RS_Identifier if a value for code space value is provided. +
 In such cases (where there is a code space provided) it is now strongly recommended to use MD_Identifier and encode the complete URI as a gmx:Anchor in the code element.