Cheers Kovid, sorry for mentioning a "file type" plugin, was typing from work without the calibre code in front of me so was relying on my bad memory
When I PM'd John about this ages ago he did wonder about there being a problem getting access to the custom columns from that plugin, hence my comments. However it could well be he also was speculating off the top of his head and I have just perputated a myth
. As you say with a metadata object there isn't really an issue.
I'll have a look on the weekend then if you aren't against the idea in principle.
@SauliusP - if you aren't in a desperate rush, you might just want to wait a day or so for me to knock this up and then just copy the relevant bits of the implementation.