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|	Available	|
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t-shirt: red, green, blue
trousers: blue, kaki, black
socks: white, black, blue

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|	List 1 - items	|
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Column 1
t-shirt
trousers
socks


---------------------------------
|	list 2 - colors		|
---------------------------------
column 1		column 2 (lookup to list 1)
red			t-shirt
green			t-shirt
blue			t-shirt
blue			trousers
kaki			trousers
black			trousers
black			socks
white			socks
blue			socks

-----------------
|	form	|
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Mulsiple selection box: Items
Dropdown: blank unles items selected from multiple selection box => then displays clolors that occur in ALL made selections.

I.E.
Multiple selection box: t-shirts, trousers
Drop Down options: blue

Multiple selection box: trousers, socks
Drop Down options: blue, black

Multiple selection box: t-shirts, trousers, socks
Drop Down options: blue