HTML, as a markup language, is a human-centered language focused on the simple structuring of data in an informative way. In that sense, it is about the transformation of data into information, and the relating of information to other information (structurally and across sets of information, in the form of links and dynamic content). When its structure is non-informative, it fails to meet it purpose for existence. When its content (the content it structures) is uninformative, disinformative, or misinformative, it fails to meet its intended ends to that extent (its use is then misuse), and this is true also of its use in wrong ways (for instance, its unsemantic, unclear, or badly or misinformatively-structured use). HTML is to inform, and when not informing it is to that extent outside of its purpose, missing the good for which it was meant. The highest value of HTML is in its human-centered informativeness.
CSS on the other hand is infographical, not the thing itself, but a transformer or purveyor of the thing into visual language. Still meant to inform, CSS focuses on informationalizing the physical reality of the HTML for presentation, as a kind of second-order information tool. As HTML applies structure to the content, so CSS applies physical instantiation (as pixels and their relations) to that structure. This physicalizing of the structure is itself informative–it is informative about the structure, while the HTML is informative about the content through its imposed structure. That content, and the informational structuring of that content is human from beginning to end, even though non-human machines are used in its processing, storage, and retrieval.
HTML is intended to apply schemas of the types of information and their relationships to one another, a sort of framework for the metaphysics of the Web of facts and thoughts; that is, it is meant to delineate the species and genus of data and information and their relations, as well as properties and their attributes of each species. CSS declares the material aspects of those things relative to that delineation. While the styles of CSS are meant to make meaning clear to humans, the focus of the language itself is on HTML and pixels and timing and change. The focus of html is on humans, on data, and on information. CSS is used by and for humans through pixels and HTML, and HTML is by and for humans as communication, a type of codification of communication events and their relations.
While HTML (and CSS) may be used by and for non-humans (for instance, computers), its purpose is information, something which cannot be created by or consumed and understood by non-human tools. It is about composition of meaning-making and mean-understanding, codification for information storage and retrieval, knowledge externalization as thoughts ordering the material world in order to be rethought, by and for humans. To speak HTML well is to bring data and information to being in a Web environment in a certain structured and intentionally informative way.
To say that HTML is human-centered is not to say that it focuses on the whole human. HTML focuses on the thought structures and informational processes of humans, not on their physical existence, their feelings, desires, or wills. Its focus is on the products and processes of rational creatures. It is a very shy language (it does not advertise itself even though it is behind the curtain in nearly all Web transactions), and is a kind of meta-informational language, a language about data and information. It is applied to language and data as a very small and simple markup, declaring which data is, and what data is. It is very weak and simplistic, and intentionally so, but more than that: it is very misused, and this against the intentions of its creators.
Use HTML to inform; stop using it to misinform. Value it for what it is, because it is meant to help you value your own very human thinking and communicating processes, to help you as you are. It is meant to be a tool for your good. That is its value. Our thinking as humans is one of our highest faculties, part of our own purpose, part of our own highest value, why we exist. Let your thoughts, words and code be valuable.
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