In order to increase performance when large number of documents is to be created in a single request (mailshot) add an ability to mark "acrofields" when editing OO document. "Acrofields" would be the places in OO templates that are likely to be different for each generated document. This would allow to separate the part of OO template which will be the same for each generated document from the part that will be different and allow better caching of documents. FOP would be used only to generate the first document while the next documents would retrieved from cache and amended with evaluated 'acrofields'.