What is the difference and relation between "Page description language", "markup language" and "Page description markup language"?
Based on their wiki webpages, I just don't understand what is their difference. Why needs there be a markup adaption of the Page description language - "Page description markup language"?
Examples: PostScript is a page description language. Is it a markup language? HTML and Latex are markup language. Are they page description language?
Based on the Wikipedia pages for both it seems that a Page description language describes how text is laid out on a page, whereas a markup language is simply a means to annotate text. This does mean that you can use a markup language to annotate the text to describe how it should be presented on a printed page, this is called a Page description markup language.
http://en.wikipedia.org/wiki/Page_description_language "a language that describes the appearance of a printed page"
http://en.wikipedia.org/wiki/Markup_language "a system for annotating a text in a way which is syntactically distinguishable from that text"
One is for printing.
One is for people.
You can think of a page description language as something like a Word file: it's got blobs of text and an idea of where to put them. A markup language is just a listing of data that provides some type of context. A good example of a markup language is HTML: it gives context to the text that you put in it, but the layout is largely variable. You're basically just telling HTML what your data should look like; you're not fine-tuning it to what it should look like exactly (that's what CSS is for).
I'll start from a "page description markup language" by quoting what Wikipedia has to say on the subject:
A page description markup language is a type of markup language that is used to describe the appearance of a printed page. It is a markup adaption of the Page description language (which is a Domain-specific programming language), and is often created using XML.
Now, a markup language, same source:
A markup language is a system for annotating a text in a way which is syntactically distinguishable from that text.
Finally, a page description language or PDL:
A page description language (PDL) is a language that describes the appearance of a printed page in a higher level than an actual output bitmap.
As I understand it, PDLs are strictly domain specific and may, but don't have to use markup to encode page contents.