Forum OpenACS Q&A: Response to db_multirow -extend and other enhancements
As far as I know the ability to append a code block to db_multirow and let it manipulate the field values before they go into the datasource was completely undocumented until now. I hope the patch also adds some explanations to the proc's documentation string.
I would like to suggest to also add the following feature to the documentation: if for any reason you want to skip a row in the resultset without adding it to the datasource, then you can call the "continue" statement within the code block. Most times it is propably better to write more accurate queries that don't return unwanted rows, but in some situations that might be useful.