Interoperability with existing use of HTML in plain text constructs

[hoehrmann]

It appears to be popular to use HTML fragments in information model items that are supposed to be plain text, including that some existing implementations happily render them as HTML instead of plain text. Random example:

• https://sdmx.oecd.org/public/rest/v2/structure/dataflow/OECD.SDD.NAD.SEEA/DSD_NAT_RES@DF_NAT_RES/1.0

SDMX implementations would struggle to interoperate for this kind of message. There is nothing unusual about plain text looking like it might be HTML, say % a<b and b>c could be rendered as-is, or as "% ac" depending on any given SDMX implementations preference or configuration.

There should be a feature for this, with suitable encoding in the SDMX formats, to allow interpretation of such texts as intended and interoperably where the format is properly indicated.

This probably also applies especially to annotations, which so far unfortunately lack format.dataType which would allow setting the format to XHTML for this, as can be done for dimensions, attributes, and measures.

(In doubt, please handle this as a public review comment on SDMX 3.1 once the comment period begins.)