[horde] Sorting Emails

[Mike Poznecki]

I want to sort my email by a field that is different than what is allowed.  According to the php website:

Criteria can be one (and only one) of the following:   
   - SORTDATE - message Date
   - SORTARRIVAL - arrival date
   - SORTFROM - mailbox in first From address
   - SORTSUBJECT - message subject
   - SORTTO - mailbox in first To address
   - SORTCC - mailbox in first cc address
   - SORTSIZE - size of message in octets
But I would like to sort by a different field.  So my questions are these:
1. When the emails are read from the server, are they cached in a place that I can then sort?  If so, are all emails brought back and cached?  If so, where in the code can I look to find where to start making my changes?
2. Is there some other way to implement a sort when calling the IMAP server? 
3. Why does Horde pass in "DISPLAYFROM"?  I cannot find anywhere in the IMAP docs that references that.