diff --git a/expat/lib/expat.h b/expat/lib/expat.h
index cfbdf2a3..dbdaaa9c 100644
--- a/expat/lib/expat.h
+++ b/expat/lib/expat.h
@@ -814,8 +814,13 @@ XML_GetErrorCode(XML_Parser parser);
 
 /* These functions return information about the current parse
    location.  They may be called from any callback called to report
-   some parse event; in this case the location is the location of
-   the first of the sequence of characters that generated the event. 
+   some parse event; in this case the location is the location of the
+   first of the sequence of characters that generated the event.  When
+   called from callbacks generated by declarations in the document
+   prologue, the location identified isn't as neatly defined, but will
+   be within the relevant markup.  When called outside of the callback
+   functions, the position indicated will be just past the last parse
+   event (regardless of whether there was an associated callback).
    
    They may also be called after returning from a call to XML_Parse
    or XML_ParseBuffer.  If the return value is XML_STATUS_ERROR then