locktime – Does the stack have access to the current block height when validating a transaction?

In the “Freeze funds until a future point” example at https://en.bitcoin.it/wiki/Script it is mentioned that “the top stack entry is checked against the current time or block height”.

Does this mean the stack can access variables like current block height and time? Or is this incorrect on the wiki? I understand when CTLV is used with nlocktime and check each other. But if I use nlocktime alone, is it a stack operation to get the current block time from the system?

So what other system level variables does the stack have access to?