[QUOTE=quartzy;1067943]What's a namespace? [quote]
each document type is described in a way, for example if we talk about xhtml, you can see in the doctype there is a url to http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd which is the description of xhtml.
Now when you look to the head element you see this:
what is yellow is the namespace for xhtml and as you can see there is nothing after xmlns, that means this is the 'default namespace'.
http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
This make it possible to write the element as you know. Now if the namespace is not declared default the html element need to be 'prefixed'.
For example using p as prefix will have:
that means that each xhtml element must have a p: in from, for example you have p:div instead of div.
:p="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
now next question could be 'why all this complication?',
the answer is simple, you can mix two type of documents, who have same name for elements. Example: having another type of document who also have defined a div element, let's say we talk about facebook, you can mix fb with xhtml:
the validator know about namespaces and test if your document follow the description of the documents. This is the short version of the story probably havy incomplete,
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"
<fb:div>this is a div but a facebook div</fb:div>
<div>this is our usual xhtml div<div>
i guess you don't need for validation purpose to make an fb account but if you want is not a big deal,
No they did not mention fb was going to be obsolete they mentioned how to add code to get the fb to validate. As I did not have an api account did not read properly.
try the solution with declaring the fb namespace and let me know if it work,