6. The method of claim 1 , wherein determining each user who authored a text portion of the document that overlaps the text span for the thread further comprises: storing for the document an author list indicating for sequential portions of text, an author of the portion and a length of the portion; comparing the selected text span with the author list to identify portions of text that overlap the text span; and determining the author of each text portion that overlaps the text span.
6. The method of claim 1 , wherein determining each user who authored a text portion of the document that overlaps the text span for the thread further comprises: storing for the document an author list indicating for sequential portions of text, an author of the portion and a length of the portion; comparing the selected text span with the author list to identify portions of text that overlap the text span; and determining the author of each text portion that overlaps the text span. 7. The method of claim 6 , wherein a text portion overlaps the text span by either i) starting before a beginning of the text span and ending after the beginning of the text span, or ii) starting between a beginning and an ending of the text span.