Impose equations on different subdomains from xml mesh

Hello,
I have a mesh file in “xml” with the associated "facet_region.xml "and “physical_region.xml”
Could you please tell me how to introduce my pdes for each domain?
Thank you

See for instance this demo. However, i would advice you to But use xml, But xdmf, as described in these two posts :

and

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Thank you very much.