expressions clarification

[Dino Edwards]

I'm trying to figure out what the difference between the following expressions 
are:

[qr'.\.(mdb)$'ix => 0]
[qr'.\.(uue)$'i => 0]
[qr'^\.(lha)$' => 0]

Mainly, trying to figure out when you put in "ix", "i" or nothing at all at the 
end of the expression.

Thanks