I wanted to implement a configuration setting for websource scripts, that controls the Preview button on the List of search results and the This Album on *some server* labeled URL on the Adjust tag information screens. The previews should show the Cover of the album in wysiwyg-manner in a browser window if the corresponding configuration option is set.
Using the (undocumented) placeholder %_preview% in
[IndexFormat]=%_coverurl%|%_preview%|%_url%|...
and supplying the coresponding URLs in the ParserScriptIndex block of the web source script works well, as long as a search for the album is needed.
But I want to use this feature also in cases where the album URL (or other album identifiers) are already known and only the ParserScriptAlbum block is used. In this case the output buffer "CurrentPreview" always contains the preview URL of the album (set from Mp3tag). If ParserScriptIndex would have been executed, the content of "CurrentPreview" were taken from %_preview% placeholder and could contain the cover URL or the album URL, depending on the configuration setting.
In ParserScriptAlbum actually it is impossible to write to the output buffer "CurrentPreview". Any attempt to change its content has no effect. So the configuration setting for cover preview only works for searches and not for already known albums. This is especially bad for web sources like [WS] Bandcamp (search by URL), that don't support searching and therefore this feature can not be implemented in such a script.
Therefore I suggest to enable a writeable output buffer "CurrentPreview" in ParserScriptIndex. There are other use cases, that request for a way to transfer arbitrary data from ParserScriptIndex into PaserScriptAlbum, and therefore could benefit from that feature, because the transferred data could be removed, e.g. [WS] Cover Art Archive by @rboss .