+'ParserOptionsRegister': Register additional parser options. Note that if you
+change the default value for an option, all existing parser cache entries will
+be invalid. To avoid bugs, you'll need to handle that somehow (e.g. with the
+RejectParserCacheValue hook) because MediaWiki won't do it for you.
+&$defaults: Set the default value for your option here.
+&$inCacheKey: To fragment the parser cache on your option, set a truthy value here.
+&$lazyLoad: To lazy-initialize your option, set it null in $defaults and set a
+ callable here. The callable is passed the ParserOptions object and the option
+ name.
+