Using JavaScript/JSON in your Ebay listings to post user selected options back to you

I am seeing some Ebay users create listings where data is dynamically sent to and fetched back from external sources. This can be a shipping calculator or some开发者_开发问答 variants you have provided for a product in a drop-down list.

See example here

Somehow data is sent to a PHP page which returns the postcode as an image

Also the upgrade drop down lists seem to send JSON objects back to a PHP page etc.

What is exactly involved in this solution and if there's a good guide/script resource for Ebay listings out there that will let me know how to do this?

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See what I did -> opened the link you posted, opened the listing description with FireBug, found the JS script withing the listing description, which is not a complicated one.
So I guess you only need to look at the script to learn what they did there.
I would guess it uses JSONP or similar techique. You can also use IFRAME b.t.w

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Javascript is not allowed in item description. The only option to do it will be using a Flash object that will communicate with a PHP/ASP page on your server (this is allowed).