XHTML1: What are "white space characters"?

Dear HTML Working Group,

  Appendix C.5 of the XHTML 1.0 Second Edition Recommendation states:

[...]
  Avoid line breaks and multiple white space characters within
  attribute values.
[...]

It is not clear to me what this refers to. What is a "white space
character" in this context? It seems that one can choose from the
definition in XML 1.0, XML 1.1, Unicode or one of the definitions
in HTML 4.01 and further differentiate between white-space characters
in the source code and white-space as character references and even
further differentiate between the white-space pre and post attribute
value normalization as defined in the XML Recommendations.

Could you, in order to remove this confusion, please provide an exact
algorithm that software could use to determine whether a document meets
that constraint?

Could you also please clarify what the exact difference between HTML
and XHTML is in this regard? This seems to be a more general
consideration for either language and thus misplaced in Appendix C.

regards.

Received on Monday, 12 July 2004 00:14:35 UTC