limiting searches to particular sources

[Fred Zimmerman]

I want to be able to list some searches to particular sources, e.g. "wiki
only", "crawled only", etc.  So I think I need to create a source field in
the schema.xml.  However, the native data for these sources does not
contain source info (e.g. "crawled").  So I want to use (I think)
<copyfield> to add a string to each data set as I import it, e.g.
"website-X-crawl".  So my question is, how do I insert a string value into
a blank field?