Which functions and features in Numbers are NOT exported correctly to Excel?

Question

I wish to know EXACTLY which functions I use in a Numbers sheet WILL FAIL to export correctly to an Excel or Neoffice spreadsheet.
For instance, I created a Numbers spreadsheet using prolific use of the IFERROR function. However, when I EXPORT to XLS, all the cells that used the IFERROR function were replaced by the literal value of the cell. My IFERROR formulae were not EXPORTED as I had expected.
I note that some formulae were converted correctly in my EXPORTED spreadsheet: eg MAX, MIN, AVERAGE.
I understand that IFERROR was a function introduced recently to Excel, ie in the 2007 version. Consequently, I suspect that Numbers exports to a pre-2007 version of Excel. If so, which version?
I have found this list that shows which functions are compatable amongst various versions of Excel:
Excel Functions: Compatibility Reference (2010, 2007 & 2003). (n.d.). Retrieved from https://docs.google.com/spreadsheet/ccc?key=0AsHau4_IeCfwdG45c0VhcjBBUGNreVo2ZzN NRU1BT0E#gid=0
This list shows that, for instance, IFERROR exisits inb both Excel 2007 and Numbers-09. So why is IFERROR not exported?
Curmi, J. (n.d.). Summary of function in excel and numbers-09. Retrieved from http://curmi.com/blog/wp-content/uploads/2009/01/functions-in-excel-and-numbers- 09.pdf
Some examples of my use of ISERROR in Numbers are as follows:
=IFERROR(RANK(C47,$C47:$J47,1),"")
=IFERROR(MEDIAN(C51:C58),"")
=IFERROR($C32-C88+1,"")
I use the above function to  carry out the calculation ONLY IF  a cell is non-blank and contains a number.
More questions
What are the rules that Numbers uses to convert to Excel?
Is Numbers converting to the 2003 version of Excel? ... or an earlier version? ... which version?
Why desn't Numbers advise me there were conversion errors or simplifications made?
eg: "Cell A33 Function IFERROR was exported to the cell value for Excel"
Is there a preference that I can select which version of Excel that Numbers will export to?
In the meantime, I must abandon Numbers and use NeoOffice!

Answer 1

Thanks,
I applied your suggested ISERROR transformation to examples such as:
=IFERROR(RANK(C47,$C47:$J47,1),"")
=IFERROR(MEDIAN(C51:C58),"")
=IFERROR($C32-C88+1,"")
However, a caution for young players....
Certainly, the ISERROR function exports to .xls. However, it behaves differently in NeoOffice.
Items 1 and 2 function identically in the case of say, ranking a row in which some cells are blanks.
Item 3, when translated using ISERROR to =IF(ISERROR(C32-C88+1),"", C32-C88+1), results in "" (ie error is raised) in Numbers but yields figure 0 in NeoOffice when there is a blank in either of the cells.
I  recall from programming school in the mid-1970s that using GOTO statements and On Error branch statements were not admissible as routine programming steps. In fact, we received an automatic fail grade if we used a GOTO or GOTO like construction. So, I have found a more programmatically elegant way to solve my problem: eg:
=IF(C88="","",C32-C88+1)
Curiously, earlier I found/suspect this does not work equivalently in Numbers and NeoOffice:
=IF(ISBLANK(C88),"",C32-C88+1)
When you try using ISBLANK you always get an intuitively unexpected result because ISBLANK ONLY gives TRUE when there is absolutely nothing in a cell. A Formula reference in the cell, even if the function result yields "", gives FALSE... because, according to the definition of ISBLANK the cell contains a formula.
As I tell my students, ALWAYS lookup the HELP on any function you use. ALWAYS test the function to see how it performs!.... and lesson 3: Always test your spreadsheet on different systems.... then hope!
FYI:
Here's a  link to my Spreadsheet (Neoffice .xls) and a video explaining its use.
Team Contribution: Introduction (Prototype). (2013). Retrieved from http://www.youtube.com/watch?v=bj87FGLoplk&feature=youtube_gdata_player 
I don't guaranteee this link for ever! ... and I continue to "tweak" it
https://www.dropbox.com/s/1jz7gzksejnbqo1/Team%20Contribution.xls