Is "." a valid xs:decimal?

Section 3.2.3.1 of XML Schema Part 2 says that for xs:decimal, "leading and
trailing zeroes are optional". Does this mean that "." is a valid
representation of the number zero?

MSXML, Xerces, and XSV all reject ".", but they seem to be doing what they
thought the spec meant to say, not what it actually says.

Michael Kay