How does collation work when printing multiple copies of a PDF portfolio?

[SoggyCornflake]

Hello,

Say you have a portfolio that combines 3 pdf files (a, b, c) of 3 pages each (1, 2, 3). So page 1 of file a is a1 in the example below, and so on.

My question is, if you print 3 copies and tick 'collate', in which order would pages come out?

a1, a2, a3, a1, a2, a3, a1, a2, a3, b1, b2, b3, b1, b2, b3, b1, b2, b3, c1, c2, c3, c1, c2, c3, c1, c2, c3

OR

a1, a2, a3, b1, b2, b3, c1, c2, c3, a1, a2, a3, b1, b2, b3, c1, c2, c3, a1, a2, a3, b1, b2, b3, c1, c2, c3

Thank you for letting me know.

[SoggyCornflake · Accepted solution]

I found out so will answer my own question in case this helps anyone.

Selecting 'collate' when printing x copies of a portfolio results in each set printing x times before moving on to the next (rather than printing the whole portfolio x times).

So as per the above example: 

a1, a2, a3, a1, a2, a3, a1, a2, a3, b1, b2, b3, b1, b2, b3, b1, b2, b3, c1, c2, c3, c1, c2, c3, c1, c2, c3

Worth noting that if a set has odd pages and you select double-side printing, the last page of the set will print correctly (i.e. what would be page 4 will be left blank).