Include Inland Revenue Authority of Singapore (IRAS) e-Tax

[krisraich]

Sources: https://www.iras.gov.sg/media/docs/default-source/uploadedfiles/pdf/iras-xml-schema-user-guide-for-crs-return-(fourth-edition).pdf

[krisraich]

There are some schemas included
https://go.gov.sg/gstinvoicenowreq-resources
gstinvoicenowreq-resources.zip

[milger-ecosio]

The linked zip file contains a schematron file (separately attached), which is what we would think is the relevant validation.

non_peppol_doc_validation.sch.txt