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. For example,
-`\[[!meta foo="bar"]]` becomes `<meta name="foo" content="bar">`. As with `name`, this
-won't be allowed if the [[!iki plugins/htmlscrubber desc=htmlscrubber]] plugin is enabled.
+`\[[!meta foo="bar"]]` becomes `<meta name="foo" content="bar">`. As
+with `name`, this won't be allowed if the [[!iki plugins/htmlscrubber
+desc=htmlscrubber]] plugin is enabled.
+
+This syntax cannot be used for meta headers with unusual names, in
+particular names containing `:` such as `flattr:id` and `twitter:card`.
+Please use `\[[!meta name="..." content="..."]]` for those headers.
[[!meta robots="noindex, follow"]]