[Template] core.viewtopic_page_header_before

Identifier: core.viewtopic_page_header_before
Parameters: any
Explanation:

Currently, there is not a proper cleanup hook. The post query can be adjusted with `viewtopic_get_post_data`. The extra data can be read with `viewtopic_post_rowset_data`and new post data can be then created, but not stored in `post_row`. This means that the data has to be stored as member of the class and then the `post_row` can be updated by `viewtopic_modify_post_row`. The array then can be unset by `viewtopic_modify_page_title`, but this will break if this part of the code is relocated during a refactoring session. The proposed handle does not have this problem, because it is placed just before the rendering process.