MobileRead Forums - View Single Post - Confused! XHTML, HTML, HTML5, EPUB2, EPUB3???

dgatwood · 02-20-2013, 12:36 AM

From the top:

SGML stands for Standard Generalized Markup Language. There are many SGMLs. Crudely put, an SGML is any markup language that is characterized by any arbitrary set of tags surrounded by angle braces, with certain bits at the beginning to tell you what type of file it is, and there are probably a few other rules.

XML is a strict subset of SGMLs. XML is a strict subset of SGMLs in which, among other things, all tags must be matched with a close tag, and a few other details. There are many dialects of XML (an XML dialect is basically just a specific set of allowed tags that can be nested in specific ways), including DocBook, XHTML, property lists, and so on.

HTML is an example of an SGML. HTML has a specific set of tags that are considered valid. HTML is not, however, based on XML, because some tags do not have to be closed at all (hr, script when a URL is provided, and so on), and some tags auto-close at the right time (p, li, etc.). [Edit: And, as Turtle91 pointed out, HTML specifies case-insensitive tag and attribute parsing, whereas XML specifies case-sensitive tag and attribute parsing, which, in the case of XHTML's built-in tags and attributes, translates to "all lowercase".]

HTML5 is a specific version of HTML. Like all HTMLs, it is an SGML, but HTML5 files are not (necessarily) proper XML.

XHTML is a special form of HTML that has been modified slightly so that every XHTML file is a proper XML file that conforms to the stricter XML standards. This requires a few tiny tweaks around the fringes, but it mostly looks like HTML with some extra close tags or self-closing tags.

XSLT is another XML dialect. An XSLT stylesheet provides a set of rules for transforming from one XML dialect to another (typically, though in practice, it can be used to translate a specified XML dialect into pretty much anything, up to and including LaTeX commands).

EPUB2 and EPUB3 are versions of EPUB. EPUB2 uses XHTML under the hood. EPUB3 uses HTML5, but it must be parseable as XML. So it must be a polyglot XML/HTML5 document. This polyglot is called XHTML5, but is defined as part of the HTML5 standard rather than in a separate standard as previous XHTML versions were.

Clear as mud?

02-20-2013, 12:36 AM	#4
dgatwood Curmudgeon Posts: 629 Karma: 1623086 Join Date: Jan 2012 Device: iPad, iPhone, Nook Simple Touch	From the top: SGML stands for Standard Generalized Markup Language. There are many SGMLs. Crudely put, an SGML is any markup language that is characterized by any arbitrary set of tags surrounded by angle braces, with certain bits at the beginning to tell you what type of file it is, and there are probably a few other rules. XML is a strict subset of SGMLs. XML is a strict subset of SGMLs in which, among other things, all tags must be matched with a close tag, and a few other details. There are many dialects of XML (an XML dialect is basically just a specific set of allowed tags that can be nested in specific ways), including DocBook, XHTML, property lists, and so on. HTML is an example of an SGML. HTML has a specific set of tags that are considered valid. HTML is not, however, based on XML, because some tags do not have to be closed at all (hr, script when a URL is provided, and so on), and some tags auto-close at the right time (p, li, etc.). [Edit: And, as Turtle91 pointed out, HTML specifies case-insensitive tag and attribute parsing, whereas XML specifies case-sensitive tag and attribute parsing, which, in the case of XHTML's built-in tags and attributes, translates to "all lowercase".] HTML5 is a specific version of HTML. Like all HTMLs, it is an SGML, but HTML5 files are not (necessarily) proper XML. XHTML is a special form of HTML that has been modified slightly so that every XHTML file is a proper XML file that conforms to the stricter XML standards. This requires a few tiny tweaks around the fringes, but it mostly looks like HTML with some extra close tags or self-closing tags. XSLT is another XML dialect. An XSLT stylesheet provides a set of rules for transforming from one XML dialect to another (typically, though in practice, it can be used to translate a specified XML dialect into pretty much anything, up to and including LaTeX commands). EPUB2 and EPUB3 are versions of EPUB. EPUB2 uses XHTML under the hood. EPUB3 uses HTML5, but it must be parseable as XML. So it must be a polyglot XML/HTML5 document. This polyglot is called XHTML5, but is defined as part of the HTML5 standard rather than in a separate standard as previous XHTML versions were. Clear as mud? Last edited by dgatwood; 02-20-2013 at 12:39 AM.