How to get block at coordinates?

[_XxFedexX_]

Basically I want to check the block below the player.
If it is stairs or piston, return true;
else return false.
I checked in the API but didn't found anything that could do this.
Thank you.

Post Scriptum: sorry for bad English, i am not mother language.

[NiLSPACE]

You can do it with this code:

local blocktype = world:GetBlock(player:GetPosition():addedY(-1));

[_XxFedexX_]

You can do it with this code:

local blocktype = world:GetBlock(player:GetPosition():addedY(-1));

I get error attempt to index local 'PlayerWorld' (a nil value)
with this code:

33 function testBlock(aPlayer, OldPosition, NewPosition)
34     local PlayerWorld = OldPosition.world -- I get error here
35     local block = PlayerWorld:GetBlock(aPlayer:GetPosition():addedY(-1))[/font]
36 end

And thank you for your support! 

[12xx12]

You can do it with this code:

local blocktype = world:GetBlock(player:GetPosition():addedY(-1));

I get error attempt to index local 'PlayerWorld' (a nil value)
with this code:

33 function testBlock(aPlayer, OldPosition, NewPosition)
34     local PlayerWorld = OldPosition.world -- I get error here
35     local block = PlayerWorld:GetBlock(aPlayer:GetPosition():addedY(-1))[/font]
[color=#d4d4d436 end[/font][/size][/color]

And thank you for your support! 

The Position object doesn't know it's world. it's only three values.
You need to ask the player object for it's world

34     local PlayerWorld = Player:GetWorld()