yogi_With VLOOKUP Function In New Google Sheets One Can Use MultiColumn Search_Key -- WOW!

                                          Google Spreadsheet   Post  #1472
Yogi Anand, D.Eng, P.E.      ANAND Enterprises LLC -- Rochester Hills MI     www.energyefficientbuild.com.   Jan-04-2014
question by mcjtom (https://productforums.google.com/forum/#!category-topic/docs/spreadsheets/SRGdEhVvdFc)

Adam's/ahab's Vlookup as array formula - multicolumn search criterion?
I was playing with the Adam's/ahab's amazing machine:

=arrayformula(iferror(vlookup($A2:$A,'Helper_01'!$A:$I,7*sign(row($A2:$A)),false)))

By mistake I change the first Vlookup argument to multi-column array (A2:B). The formula still worked, but what does it actually do?  

Is the first column of 'Helper_01'!A:I range compared to either of both columns of the A2:B search criterion, or just one of them (but which one)?

Cheers!

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as of Jan-08-2014 I have noticed there is a problem displaying Google New Sheets in my blog posts

so in case my spreadsheet is not being displayed in the blog post, I am posting an image of the spreadsheet  as well