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The block will be saved in XHTML property like this
<div data-classid="36f4349b-8093-492b-b616-05d8964e4c89" data-contentguid="44748655-f81e-4e3d-910a-5e11b273f8ac" data-contentname="New Block">{}</div>
So if you can just export and import as normal. However you will also to export and import CMS content (which includes the blocks) to make the properties work.
I'm using the Service API's catalog bulk import service to import a catalog via XML files. My, say, Product class has a property that is a block, and I would like to import data into the property block's properties.
For example, say I have a Product type with an Address property that is an AddressBlock (this is not a real example)...
How would I import the address properties via the catalog bulk import? The XSD-generated classes aren't giving me any clues.