stored state, call `getstate("page", "id", "key")`, and to store state,
call `setstate("page", "id", "key", "value")`.
+To access ikiwiki's ARGV array, call `getargv()`. To change its ARGV, call
+`setargv(array)`.
+
## Notes on function parameters
The [[plugin_interface_documentation|write]] talks about functions that take
to convert these named parameters into something more natural for the
language as part of their XML RPC interface.
+## undef
+
+XML RPC has a limitation that it does not have a way to pass
+undef/NULL/None. There is an extension to the protocol that supports this,
+but it is not yet available in the [[cpan XML::RPC]] library used by
+ikiwiki.
+
+Until the extension is available, ikiwiki allows undef to be communicated
+over XML RPC by passing a sentinal value, a hash with a single key "null"
+with a value of an empty string. External plugins that need to communicate
+null values to or from ikiwiki will have to translate between undef and
+the sentinal.
+
## Function injection
Some parts of ikiwiki are extensible by adding functions. For example, the
FormBuilder perl objects), or use it to call `template()` (which returns a
perl HTML::Template object).
-Also. the `getopt` hook doesn't work, as ARGV is not available to the external
-plugin.
-
## Performance issues
Since each external plugin is a separate process, when ikiwiki is