Use of colon in ID

Hi,

I'm curious about the use of the colon character (":") in IDs -
As far as I can tell the spec says that they are permitted but not 
recommended.
Xerces 1.4.0's XMLCharacterProperties.validName method returns true for
IDs containing ||colons - yet when the document is parsed an error is 
returned.

Anyone know the status on the use of colons in IDs?

Thanks,
Justin.