contents. In particular, it does not check the values against the set of
valid values but serves whatever you pass it.
+* guid
+
+ Specifies a globally unique ID for a page. This guid should be a URI
+ (in particular, it can be `urn:uuid:` followed by a UUID, as per
+ [[!rfc 4122]]), and it will be used to identify the page's entry in RSS
+ and Atom feeds. If not given, the default is to use the page's URL as its
+ guid.
+
+ This is mostly useful when a page has moved, to keep the guids for
+ pages unchanged and
+ [[avoid_flooding_aggregators|tips/howto_avoid_flooding_aggregators]].
+
If the field is not one of the above predefined fields, the metadata will be
written to the generated html page as a <meta> header. However, this
won't be allowed if the [[htmlscrubber]] is enabled, since it can be used to