Have you ever seen usage of <span> like this?

Question

<span content="2010-01-08 21:35:12" property="dc:date">

What does it mean?

Answer 1

I would say it appears to be meta-information for whatever goes within the span, or it's storing values for Javascript to use at a later time, or both.

Seeing the "dc" makes me think that there may be more crucial bits that aren't included in your example.

Answer 2

Those aren't standard tags, but they are probably used by some javascript on the page that can search based on those properties, or they are akin to comments that the programmer is inserting in the html output.

Answer 3

It's a kind of meta data implementation. "dc" stands for Dublin Core which is a meta data implementation standard.

The appropriate software that can read these meta tags will know to look for a span element and then use the property and content attributes to retrieve the relevant information.

Answer 4

It seems to be XHML with Dublin Core metadata, a set of metadata field standards.

In HTML, Dublin Core info is used in meta and link elements only, and I can not find any instance where the data is validly used in a span element. Also, the content attribute is not valid in HTML. See Expressing Dublin Core in HTML/XHMTL meta and link elements.

The case is different with XHTML: As @tomlog points out in his comment, the notation you quote is used in this example on Wikipedia.