I don't think it uses some special type in any way. Rather, if you use sxml to build html in scheme and have a node in there that is a string, then the natural way to serialize this sxml into html will be to safely quote the string. Afterall, if you wanted html tags to be preserved and interpreted in the output, you would first parse the string into sxml and put that into your document. This is the difference between working with structured data vs. plain string interpolation.

But of course this only applies when you use sxml. Artanis apparently can also use plain strings or templates as responses, in which case you will have to take care of safely encoding things too.

SXML is a fairly old thing, but it isn't really typed. [0]

Rather, things are structured, so it's more like a in-memory representation of XML. It doesn't need to be serialised, only deserialised into XML's text syntax. In which case, each piece knows how it needs to be encoded.

           '(h1 (@ (id "greeting")) "Hi, there")

Its just lists of Symbol types, and string or other type values.

[0] https://en.m.wikipedia.org/wiki/SXML