Anne van Kesteren's weblog has been home lately to a few fantastic posts related to important differences between XHTML 1.0 Strict and XHTML 1.1. We're repeating a few here for future reference.
Media Types
From the W3C's August 2002 note on XHTML Media Types:
'application/xhtml+xml' SHOULD be used for serving XHTML documents to XHTML user agents. Authors who wish to support both XHTML and HTML user agents MAY utilize content negotiation by serving HTML documents as 'text/html' and XHTML documents as 'application/xhtml+xml'.
Specifically of interest is that XHTML 1.1 SHOULD NOT be served as text/html.
Further Reading:
text/html and application/xhtml+xmlCharset
From XHTML Media Types:
Therefore, while it is STRONGLY RECOMMENDED to specify an explicit charset parameter through a higher-level protocol, authors SHOULD include the XML declaration (e.g. <?xml version="1.0" encoding="EUC-JP"?>).
And from the XHTML 1.1 spec:
XHTML document authors are strongly encouraged to use XML declarations in all their documents. Such a declaration is required when the character encoding of the document is other than the default UTF-8 or UTF-16.
Further Reading:
Stylesheets
From XHTML Media Types:
The XML stylesheet PI SHOULD be used to associate style sheets.
Further Reading:
meta http-equiv
From XHTML Media Types:
Note that a meta http-equiv statement will not be recognized by XML processors, and authors SHOULD NOT include such a statement in an XHTML document served as 'application/xml' (and 'application/xhtml+xml' as well for that matter).
Jacques Distler asks: "Is it bogus just for setting the content-type and charset, or are all such declarations bogus?" There's every indication that this rule applies only to setting the content-type and charset.
Further Reading:
<html> id attribute
From a post to www-validator@w3.org
XHTML 1.1 is based on XHTML Modularization and thus disallows <html id='...' ...> XHTML 1.0 *Second Edition* had been changed in this respect and allows the html element to have an id attribute.
Further Reading:
<html id=""> by Anne van KesterenWe use Anne van Kesteren's solution -- an internal subset of the DOCTYPE -- to extend XHTML. There has been some question as to whether browsers, Internet Explorer specifically, will resort to Quirks Mode in the face of custom DTDs or extended DOCTYPEs. (Keep in mind that Gecko browsers SHOULD, in the parlance of the W3C, get documents served using the application/xhtml+xml media type, which invokes Standards Mode in those browsers every time.) This is most likely not an issue. Much more information on this subject is available: Extending XHTML: Target and Strict.
You may also get some mileage out of this list of changes to XHTML between versions 1.0 Strict and 1.1.
We'll add to this list if necessary. For the record, the XHTML 1.1 version of our home page currently meets all the above requirements