Markup languages are memes as well as memetic, semantic and sometimes mimetic systems.
(Within XML, think TEI, Docbook, NLM/JATS, DITA, MODS/METS, vertical schemas. HTML, fer chrissake. Markdown. Grammar-based formats. Object property sets. Application binaries.)
I have written about markup languages considered as games; they can also be considered as genes. Indeed one might see a document (here in the very narrow, XML/SGML sense of that word) as phenotype to a schema’s genotype. The fact that formally, documents are always already valid to infinities of unspecified schemas (since an infinite number of valid schemas can be trivially and arbitrarily generated for a given document), obscures the fact that “in the real world” (that is, in the wider contexts of our knowing of it), a document does not stand merely as a formal abstraction (a collection of element types), but also has a history. As such, it is representative of its history as it is of its (purported) representations. That is, the aircraft maintenance manual is not only a description of an aircraft; it is also a maintenance manual. This history, often, implicates a particular schema.
- Replicate (are copied across file systems)
- Are modified and adapted
- May be identified with “species”, which evolve over time
- Are embedded in local systems, but also enable discrete semantic “environments” (which may be portable)
- Occasionally cross the barriers between systems (often to be adapted on the other side)
- Sometimes include mechanisms for their own adaptation
(BTW these are also all true of documents, at a more discrete level. Indeed, schemas are among the mechanisms that documents provide for their own adaptation. Note how you can stretch the concepts of “document” and “schema” here very widely, to all kinds of media, especially if you allow for the idea that schemas may exist implicitly without being codified.)
Unlike living systems (but perhaps like viruses), schemas cannot be said to have volition of their own. They get their volition from the environments in which they are promulgated. Perhaps they are more plant-like than animal-like.
Also the question arises as to whether (and to what extent) they are parasitic or symbiotic. One suspects they have to be symbiotic in order to encourage adoption. However, they clearly get much of their power from their network effects (the more people using HTML, the more useful HTML becomes to use) — and at a certain point, this may introduce stresses between the local goals (of HTML users themselves) and of the interests that promote HTML despite poor fitness to local goals.
Schemas are also the deliberate, logical/social/linguistic creations of people and of organizations of people. Can they be this, and also “viral” at the same time?