XData blocks in Caché classes has a MimeType property, and dcoumentation says
MimeType — The MIME type (more formally, the internet media type) of the contents of the XData block. The default is text/xml
A programming language is a formal language that specifies a set of instructions that can be used to produce various kinds of output. Programming languages generally consist of instructions for a computer. Programming languages can be used to create programs that implement specific algorithms.
It's a general tag that covers the topics related to programming with InterSystems Data Platform using different languages.