method FindAt(position As %Integer, target As %RawString,
   ByRef tmpstr As %RawString = "", caseinsensitive As %Boolean = 0) as %Integer

Find the first occurrence of target in the stream, starting the search at position.
The method returns the position of this match, counting from the beginning of 
the stream, and leaves the stream positioned at an indeterminate location. 
If it does not find the target string, it returns -1.

If position=-1 then it starts searching from the location found in the 
previous search and returns the offset from the last search. 
This is useful for searching through the entire file. 
If you are doing this, you should pass in tmpstr by reference in every call. 
This is used to store the last buffer read, so the next call will start 
where the last one left off. 
If caseinsensitive=1 then the search will be case insensitive, 
rather than the default case-sensitive search.