Quoted from http://xml-tips.assistprogramming.com/sgml-xml-html-xhtml-all-together.html:

XHTML is the basis for a family of future document types that extend and subset HTML.

I understand subset here is a verb. Does it mean XHTML is a subset of HTML or HTML is a subset of XHTML?


4 Answers 4


Both previous answers have pretended (implicitly) that the text read

XHTML […] subsets HTML.

But in fact, the sentence reads (again, only the relevant fragment):

… document types that … subset HTML.

It’s those document types that, each on its own, are subsets of HTML. This explains the apparent contradiction that XHTML both extends and subsets HTML: parts of XHTML extend HTML, whereas other parts are subsets of HTML. (As an example of an XHTML document type that extends HTML, consider XForms, and for a subset of HTML, consider XHTML 1.0 strict.)

Either way, the usage of “subset” as a verb is meant to mean “be a subset of”.


It means that XHTML is a subset of HTML.

  • XHTML is the basis for a family of future document types, therefore:
  • XHTML is in this family of documents
  • these documents extend and subset HTML, therefore:
  • XHTML subsets HTML, therefore:
  • XHTML is a subset of HTML
  • XHTML is also a subset of XML. ehow.com/facts_7184267_xht-file-extension_.html. Just thought it might be worth mentioning.
    – whirlwin
    Jul 16, 2011 at 12:48
  • @Whirlwin and RIMMER: So XHTML is a subset of the intersection of HTML and XML?
    – Tim
    Jul 16, 2011 at 12:58
  • I'm not sure about HTML, but since XHTML is written in XML, I'd say it's a subset of XML, rather.
    – whirlwin
    Jul 16, 2011 at 13:04
  • 4
    No, there are two verbs in the sentence: extend and subset. Put together, I believe the author intended this to mean that XHTML drops some valid commands from HTML (the subsetting part) and adds others (the extending part), so there is no containment relationship between HTML and XHTML. This was not a well-conceived sentence. Jul 16, 2011 at 13:04

The word subset is not a verb in standard English. In this document (and others I've looked at on the web) subsetting a programming language is defined as requiring programmers to follow programming standards that only use a subset of commands. Thus,

XHTML is a markup language that subsets HTML.

would mean that XHTML is a subset of HTML. This contradicts the verb extends, which is also in the sentence. Since XHTML both extends and subsets HTML, the original sentence implies that there is in fact no containment relationship betwen HTML and XHTML.

Note that if you're talking about databases or data mining, rather than programming languages, subsetting means something slightly different.

  • 1
    Is there a word for using a noun as a verb, like we see in this question?
    – Alan
    Jul 16, 2011 at 13:51
  • @Alan: "verbing" perhaps?
    – John Smith
    Jul 16, 2011 at 15:46

For it to mean anything as a verb, per se, it must mean "setting under" (setting in inferior or subsumed position). If, as a coinage it comports differently with the subject topic, then its use as a verb can be accepted only as respects the programmers argot. Otherwise, without the ellipses, it is at best is a miss-usage for some perceived useful effect.

  • This is nonsense. You can't dictate what a word "must" mean in defiance of what people actually use it to mean. Clearly in OP's example, to subset means to facilitate the creation of subsets. Equally clearly, as @Peter Shor points out, the terns can be pressed into service to mean enforce the use of a subset with no danger of ambiguity, even though it's not generally recognised as a "standard" English verb. Nov 23, 2012 at 2:55
  • That was...; not this is.... Sorry, I did't mean to get anyone all theatrical. Thanks for the point.
    – lex
    Nov 23, 2012 at 12:56

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