SDK-Supplied Implementation for IID_ITEXTATTRWIDESTRING?

I want to invisibly tag some text by creating a text attribute boss that aggregates the IID_ITEXTATTRWIDESTRING interface, as described at http://support.adobe.com/devsup/devsup.nsf/docs/53962.htm.

Should I write my own implelemtation of IID_IITEXTATTRWIDESTRING, or is there an SDK-supplied implementation?

For example, IID_ITEXTATTRBOOLEAN has the SDK-supplied kTextAttrBooleanOffImpl implementation, although it isn't documented anywhere that I know of -- I only know about it because it's used in one of the sample plugins.

Thanks for any info.

Bob