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GlobalPal said

I'm trying to establish for legal reasons when a page was first published. I think "DCTERMS:issued" is probably it?

Do you mean in the list of meta tags? Each site can set its own meta tags as it wishes, so the significance of the tag's name and value depend on the site.

Thanks,

so is there a sure-fire way of establishing on what date/time a page was first published?

Or are you saying that it depends on how the site uses meta tags?

(do sites have to abide by the DCMI definitions, so if they choose to use DCTERMS:issued it has an agreed understood meaning?)

GlobalPal said

so is there a sure-fire way of establishing on what date/time a page was first published?

As far as I know, you cannot tell that from the client side, and you might not be able to tell without logs of changes on the server side.

(do sites have to abide by the DCMI definitions, so if they choose to use DCTERMS:issued it has an agreed understood meaning?)

I would be surprised if there were a law requiring that, but you probably can search for information as easily as I can.